Method for interaction between layers in wireless communication system and apparatus therefor

ABSTRACT

A method for forwarding a non-access stratum (NAS) message of a user equipment (UE) in a wireless communication system is disclosed. The method includes sending an uplink (UL) NAS message including a session management (SM) message to an access and mobility management function (AMF), and receiving, from the AMF, an indication message indicating that the SM message is unroutable, wherein indication information indicating that the SM message is unroutable is delivered to a SM sublayer of the UE.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly to a method for handling a NAS message with aforwarding/routing failure through interaction/information exchangebetween layers and a device therefor.

BACKGROUND ART

A mobile communication system has been developed to provide a voiceservice while guaranteeing activity of a user. However, the mobilecommunication system extends an area up to a data service as well as avoice and at present, a short phenomenon of a resource is caused due toan explosive increase of traffic and uses require a higher-speedservice, and as a result, a more developed mobile communication systemis required.

Requirements of a next-generation mobile communication system largelyneed to support accommodation of explosive data traffic, an epochalincrease of transmission rate per user, accommodation of thesignificantly increased number of connection devices, very lowend-to-end latency, and high energy efficiency. To this end, varioustechnologies have been researched, which include dual connectivity,massive multiple input multiple output (MIMO), in-band full duplex,non-orthogonal multiple access (NOMA), super wideband supporting, devicenetworking, and the like.

Particularly, for the device in which power consumption significantlyinfluences on the life of the device, various techniques for decreasingthe power consumption has been vigorously developed.

DISCLOSURE Technical Problem

An object of the present invention is to propose a method for properlyprocessing/handling, at a UE side and a network side, arouting/forwarding failure situation of a SM message at an AMF that mayoccur as MM and SM functions are separated in a new wirelesscommunication system.

Embodiments are proposed to describe a method and a device for solvingthe above-described technical problems. Technical problems to be solvedby the present invention are not limited by the above-mentionedtechnical problems, and other technical problems which are not mentionedabove can be clearly understood from the following description by thoseskilled in the art to which the present invention pertains.

Technical Solution

In one aspect of the present invention, there is provided a method forforwarding a non-access stratum (NAS) message of a user equipment (UE)in a wireless communication system, the method comprising sending anuplink (UL) NAS message including a session management (SM) message toan access and mobility management function (AMF); and receiving, fromthe AMF, an indication message indicating that the SM message isunroutable, wherein indication information indicating that the SMmessage is unroutable is forwarded to a SM sublayer of the UE.

The SM message may be generated in the SM sublayer and may be forwardedto a MM sublayer that is a lower layer of the SM sublayer. The UL NASmessage including the SM message may be sent to the AMF by the MMsublayer.

The SM sublayer may correspond to a sublayer that is defined for aprotocol data unit (PDU) session control in the UE, and the MM sublayermay correspond to a sublayer that is defined for a mobility control ofthe UE in the UE.

The method may further comprise starting a pre-configured timer, if theSM sublayer forwards the SM message to the MM sublayer; and stopping thetimer and stopping a procedure related to the SM message, if theindication information is received from the MM sublayer before the timerexpires.

The method may further comprise retransmitting, by the SM sublayer, theSM message to the MM sublayer by a predetermined number of times, if thetimer expires; and stopping a procedure related to the SM message, ifthe retransmission by the predetermined number of times fails.

The UL NAS message may further include a data network name (DNN) and/orsingle network slice selection assistance information (S-NSSAI) used forthe selection of a session management function (SMF) to forward the SMmessage.

If the SM message is a message requesting an establishment of the PDUsession, the UL NAS message may further include a PDU session identifier(ID) for the PDU session to which the establishment is requested.

The MM sublayer may forward, to the SM sublayer, information aboutwhether the unroutable SM message is permanent or temporary, togetherwith the indication information.

If the unroutable SM message is permanent, the SM sublayer may perform arelease procedure for a PDU session and/or a data network (DN) relatedto the SM message.

The SM sublayer may include the PDU session and/or the DN in a procedureforbidden list and manage the PDU session and/or the DN.

If services related to the PDU session and/or the DN are required, theSM sublayer may request a deregistration to the MM sublayer.

In another aspect of the present invention, there is provided a userequipment (UE) performing an interworking method between networks in awireless communication system, the UE comprising a communication moduleconfigured to transmit and receive a signal; and a processor configuredto control the communication module, wherein the processor is configuredto send an uplink (UL) NAS message including a session management (SM)message to an access and mobility management function (AMF), andreceive, from the AMF, an indication message indicating that the SMmessage is unroutable, wherein indication information indicating thatthe SM message is unroutable is delivered to a SM sublayer of the UE.

The SM message may be generated in the SM sublayer and may be forwardedto a MM sublayer that is a lower layer of the SM sublayer. The UL NASmessage including the SM message may be sent to the AMF by the MMsublayer.

The SM sublayer may correspond to a sublayer that is defined for aprotocol data unit (PDU) session control in the UE, and the MM sublayermay correspond to a sublayer that is defined for a mobility control ofthe UE in the UE.

The SM sublayer may be configured to start a pre-configured timer, ifthe SM sublayer forwards the SM message to the MM sublayer, and stop thetimer and stop a procedure for establishing the PDU session, if theindication information is received from the MM sublayer before the timerexpires.

Advantageous Effects

Since embodiments of the present invention enableinteraction/information exchange between NAS layers/entities inpreparation for various message forwarding/routing failure situationsthat may occur when a SM layer procedure and a MM layer procedure in 5GSand 5GC are independently separated and are simultaneously performed,they can improve message forwarding reliability/efficiency of a UE and anetwork and solve various problems resulting from the messageforwarding/routing failure.

Effects obtainable from the present invention are not limited by theeffects mentioned above, and other effects which are not mentioned abovecan be clearly understood from the following description by thoseskilled in the art to which the present invention pertains.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention as a part of detailed descriptions,illustrate embodiment(s) of the invention and together with thedescriptions, serve to explain the technical principles of theinvention.

FIG. 1 illustrates an Evolved Packet System (EPS) to which the presentinvention can be applied.

FIG. 2 illustrates one example of an Evolved Universal Terrestrial RadioAccess Network (E-UTRAN) to which the present invention can be applied.

FIG. 3 illustrates structures of an E-UTRAN and an EPC in a wirelesscommunication system to which the present invention may be applied.

FIG. 4 illustrates a radio interface protocol structure between a UE andan E-UTRAN in a wireless communication system to which the presentinvention may be applied.

FIG. 5 illustrates an S1 interface protocol structure in a wirelesscommunication system to which the present invention may be applied.

FIG. 6 illustrates a physical channel structure in a wirelesscommunication system to which the present invention may be applied.

FIG. 7 illustrates an EMM and ECM states in a wireless communicationsystem to which the present invention may be applied.

FIG. 8 illustrates a contention-based random access procedure in awireless communication system to which the present invention may beapplied.

FIG. 9 illustrates a 5G system architecture using reference pointrepresentation.

FIG. 10 illustrates a 5G system architecture using a service-basedrepresentation.

FIG. 11 illustrates an NG-RAN architecture to which the presentinvention may be applied.

FIG. 12 illustrates a wireless protocol stack to which the presentinvention may be applied.

FIG. 13 illustrates a protocol stack between a UE and a core network of5G/NR system to which the present invention is applicable.

FIG. 14 illustrates an RM state model to which the present invention maybe applied.

FIG. 15 illustrates a CM state model to which the present invention maybe applied.

FIG. 16 illustrates a classification and user plane marking for a QoSflow and a mapping of QoS flows to AN resources according to anembodiment of the present invention.

FIG. 17 is a flow chart illustrating a registration procedure applicableto the present invention.

FIG. 18 is a flow chart illustrating a NAS message redirection procedureto which the present invention is applicable.

FIG. 19 illustrates a control plane protocol stack of a UE applicable tothe present invention.

FIG. 20 illustrates a control plane protocol stack within a UE accordingto an embodiment of the present invention.

FIG. 21 illustrates a control plane protocol stack within a UE accordingto an embodiment of the present invention.

FIG. 22 is a flow chart illustrating an application example of inventionproposal 2 if PDU session synchronization fails.

FIG. 23 is a flow chart illustrating a method for sending a NAS messageof a UE according to an embodiment of the present invention.

FIG. 24 is a flow chart illustrating a method for sending a NAS messageof an AMF according to an embodiment of the present invention.

FIG. 25 illustrates a block configuration diagram of a communicationdevice according to an embodiment of the present invention.

FIG. 26 illustrates a block configuration diagram of a communicationdevice according to an embodiment of the present invention.

MODE FOR INVENTION

The present invention proposes a method for efficiently performing aninterworking procedure between an EPC and a 5G core in a wirelesscommunication system. In particular, the present invention proposes asolution in terms of a network node in order to reduce the load imposedon a user equipment (UE) in the interworking procedure.

There is provided an embodiment of a method and an apparatus for solvingthe above technical problems. It is to be understood that both theforegoing general description and the following detailed description areexemplary and explanatory and are not to be construed as limiting theinvention as defined by the appended claims and their equivalents.

Technical Solution

According to an aspect of the present invention, there is provided aninterworking method between networks of a user equipment (UE) in awireless communication system, including: performing a firstinterworking procedure for changing the network of the user equipmentfrom a 5-generation core network (5GC) network to an evolved packet core(EPC) network, wherein the performing of the first interworkingprocedure includes, if an interface between the 5GC and the EPC networkdoes not exist: receiving a first instruction from an access andmobility management function (AMF) of the 5GC network; and performing ahandover access procedure within the EPC network based on the firstinstruction.

The performing of the first interworking procedure may include, if theinterface between the 5GC and the EPC network exists: not receiving thefirst instruction from the AMF; and performing a tracking area update(TAU) procedure within the EPC network.

A packet data unit (PDU) session generated for the user equipment withinthe 5GC may be transferred to the EPC network through the handoveraccess procedure or the TAU procedure.

The performing of the handover access procedure may include:transmitting a PDN connection request message in which a request type isset to a handover, to an mobility management entity (MME) of the EPC.

The interworking method may further include: transmitting, to the MME,information indicating that the user equipment moves from the 5GC.

The EPC may have an EPC-GUTI (globally unique temporary user equipmentidentity) mapped with the GUTI of the 5GC.

The interworking method may further include, if the interface betweenthe 5GC and the EPC network does not exist and the user equipment is ina connected mode in the 5GC: performing radio resource control (RRC)release with a NG (next-generation)-RAN (radio access network) of the5GC and camping on a cell connected to the EPC.

The interworking method may further include: performing a secondinterworking procedure for changing the network of the user equipmentfrom the EPC network to the 5GC network, wherein the performing of thesecond interworking procedure includes, if the interface between the 5GCand the EPC network does not exist: receiving a second instruction froma mobility management entity (MME) of the EPC network; and performing aregistration procedure within the 5GC network based on the secondinstruction.

A packet data unit (PDU) session generated for the user equipment withinthe EPC may be transferred to the 5GC network through the registrationprocedure.

The registration procedure may be a registration procedure in which aregistration type is set to a mobility registration update.

The interworking method may further include: transmitting, to the AMF,information indicating that the user equipment is moved from the EPC.

The 5GC may have a 5GC-GUTI (globally unique temporary user equipmentidentity) mapped with the GUTI of the EPC.

The interworking method may further include, if the interface betweenthe 5GC and the EPC network does not exist and the user equipment is ina connected mode in the 5GC: performing radio resource control (RRC)release with an E-UTRAN (evolved universal terrestrial radio accessnetwork) of the EPC.

According to another aspect of the present invention, there is provideda user equipment (UE) for performing an interworking method betweennetworks in a wireless communication system, including: a communicationmodule configured to transmit and receive signals; and a processorconfigured to control the communication module, wherein the processorperforms a first interworking procedure for changing the network of theuser equipment from a 5-generation core network (5GC) network to anevolved packet core (EPC) network, wherein, if an interface between the5GC and the EPC network does not exist, the user equipment: receives aninstruction from an access and mobility management function (AMF) of the5GC network; and performs a handover access procedure within the EPCnetwork based on the instruction.

If the interface between the 5GC and the EPC network exists, theprocessor may not receive the instruction from the AMF and may perform atracking area update (TAU) procedure within the EPC.

MODE FOR INVENTION

In what follows, preferred embodiments according to the presentinvention will be described in detail with reference to appendeddrawings. The detailed descriptions provided below together withappended drawings are intended only to explain illustrative embodimentsof the present invention, which should not be regarded as the soleembodiments of the present invention. The detailed descriptions belowinclude specific information to provide complete understanding of thepresent invention. However, those skilled in the art will be able tocomprehend that the present invention can be embodied without thespecific information.

For some cases, to avoid obscuring the technical principles of thepresent invention, structures and devices well-known to the public canbe omitted or can be illustrated in the form of block diagrams utilizingfundamental functions of the structures and the devices.

A base station in this document is regarded as a terminal node of anetwork, which performs communication directly with a UE. In thisdocument, particular operations regarded to be performed by the basestation may be performed by a upper node of the base station dependingon situations. In other words, it is apparent that in a networkconsisting of a plurality of network nodes including a base station,various operations performed for communication with a UE can beperformed by the base station or by network nodes other than the basestation. The term Base Station (BS) can be replaced with a fixedstation, Node B, evolved-NodeB (eNB), Base Transceiver System (BTS), orAccess Point (AP). Also, a terminal can be fixed or mobile; and the termcan be replaced with User Equipment (UE), Mobile Station (MS), UserTerminal (UT), Mobile Subscriber Station (MSS), Subscriber Station (SS),Advanced Mobile Station (AMS), Wireless Terminal (WT), Machine-TypeCommunication (MTC) device, Machine-to-Machine (M2M) device, orDevice-to-Device (D2D) device.

In what follows, downlink (DL) refers to communication from a basestation to a terminal, while uplink (UL) refers to communication from aterminal to a base station. In downlink transmission, a transmitter canbe part of the base station, and a receiver can be part of the terminal.Similarly, in uplink transmission, a transmitter can be part of theterminal, and a receiver can be part of the base station.

Specific terms used in the following descriptions are introduced to helpunderstanding the present invention, and the specific terms can be usedin different ways as long as it does not leave the technical scope ofthe present invention.

The technology described below can be used for various types of wirelessaccess systems based on Code Division Multiple Access (CDMA), FrequencyDivision Multiple Access (FDMA), Time Division Multiple Access (TDMA),Orthogonal Frequency Division Multiple Access (OFDMA), Single CarrierFrequency Division Multiple Access (SC-FDMA), or Non-Orthogonal MultipleAccess (NOMA). CDMA can be implemented by such radio technology asUniversal Terrestrial Radio Access (UTRA) or CDMA2000. TDMA can beimplemented by such radio technology as Global System for Mobilecommunications (GSM), General Packet Radio Service (GPRS), or EnhancedData rates for GSM Evolution (EDGE). OFDMA can be implemented by suchradio technology as the IEEE 802.11 (Wi-Fi), the IEEE 802.16 (WiMAX),the IEEE 802-20, or Evolved UTRA (E-UTRA). UTRA is part of the UniversalMobile Telecommunications System (UMTS). The 3rd Generation PartnershipProject (3GPP) Long Term Evolution (LTE) is part of the Evolved UMTS(E-UMTS) which uses the E-UTRA, employing OFDMA for downlink and SC-FDMAfor uplink transmission. The LTE-A (Advanced) is an evolved version ofthe 3GPP LTE system.

Embodiments of the present invention can be supported by standarddocuments disclosed in at least one of wireless access systems includingthe IEEE 802, 3GPP, and 3GPP2 specifications. In other words, among theembodiments of the present invention, those steps or parts omitted forthe purpose of clearly describing technical principles of the presentinvention can be supported by the documents above. Also, all of theterms disclosed in this document can be explained with reference to thestandard documents.

To clarify the descriptions, this document is based on the 3GPPLTE/LTE-A, but the technical features of the present invention are notlimited to the current descriptions.

Terms used in this document are defined as follows.

-   -   Universal Mobile Telecommunication System (UMTS): the 3rd        generation mobile communication technology based on GSM,        developed by the 3GPP    -   Evolved Packet System (EPS): a network system comprising an        Evolved Packet Core (EPC), a packet switched core network based        on the Internet Protocol (IP) and an access network such as the        LTE and UTRAN. The EPS is a network evolved from the UMTS.    -   NodeB: the base station of the UMTS network. NodeB is installed        outside and provides coverage of a macro cell.    -   eNodeB: the base station of the EPS network. eNodeB is installed        outside and provides coverage of a macro cell.    -   Home NodeB: It is installed indoors as a based station, and the        coverage is a micro cell scale.    -   Home eNodeB: It is installed indoors as a base station of the        EPS network, and the coverage is a micro cell scale.    -   User Equipment (UE): A UE can be called a terminal, Mobile        Equipment (ME), or Mobile Station (MS). A UE can be a portable        device such as a notebook computer, mobile phone, Personal        Digital Assistant (PDA), smart phone, or a multimedia device; or        a fixed device such as a Personal Computer (PC) or        vehicle-mounted device. The term UE may refer to an MTC terminal        in the description related to MTC.    -   IP Multimedia Subsystem (IMS): a sub-system providing multimedia        services based on the IP    -   International Mobile Subscriber Identity (IMSI): a globally        unique subscriber identifier assigned in a mobile communication        network    -   Machine Type Communication (MTC): communication performed by        machines without human intervention. It may be called        Machine-to-Machine (M2M) communication.    -   MTC terminal (MTC UE or MTC device or MRT apparatus): a terminal        (e.g., a vending machine, meter, and so on) equipped with a        communication function (e.g., communication with an MTC server        through PLMN) operating through a mobile communication network        and performing the MTC functions.    -   MTC server: a server on a network managing MTC terminals. It can        be installed inside or outside a mobile communication network.        It can provide an interface through which an MTC user can access        the server. Also, an MTC server can provide MTC-related services        to other servers (in the form of Services Capability Server        (SCS)) or the MTC server itself can be an MTC Application        Server.    -   (MTC) application: services (to which MTC is applied) (for        example, remote metering, traffic movement tracking, weather        observation sensors, and so on)    -   (MTC) Application Server: a server on a network in which (MTC)        applications are performed    -   MTC feature: a function of a network to support MTC        applications. For example, MTC monitoring is a feature intended        to prepare for loss of a device in an MTC application such as        remote metering, and low mobility is a feature intended for an        MTC application with respect to an MTC terminal such as a        vending machine.    -   MTC user: an MTC user uses a service provided by an MTC server.    -   MTC subscriber: an entity having a connection relationship with        a network operator and providing services to one or more MTC        terminals.    -   MTC group: an MTC group shares at least one or more MTC features        and denotes a group of MTC terminals belonging to MTC        subscribers.    -   Services Capability Server (SCS): an entity being connected to        the 3GPP network and used for communicating with an MTC        InterWorking Function (MTC-IWF) on a Home PLMN (HPLMN) and an        MTC terminal. The SCS provides the capability for a use by one        or more MTC applications.    -   External identifier: a globally unique identifier used by an        external entity (for example, an SCS or an Application Server)        of the 3GPP network to indicate (or identify) an MTC terminal        (or a subscriber to which the MTC terminal belongs). An external        identifier comprises a domain identifier and a local identifier        as described below.    -   Domain identifier: an identifier used for identifying a domain        in the control region of a mobile communication network service        provider. A service provider can use a separate domain        identifier for each service to provide an access to a different        service.    -   Local identifier: an identifier used for deriving or obtaining        an International Mobile Subscriber Identity (IMSI). A local        identifier should be unique within an application domain and is        managed by a mobile communication network service provider.    -   Radio Access Network (RAN): a unit including a Node B, a Radio        Network Controller (RNC) controlling the Node B, and an eNodeB        in the 3GPP network. The RAN is defined at the terminal level        and provides a connection to a core network.    -   Home Location Register (HLR)/Home Subscriber Server (HSS): a        database provisioning subscriber information within the 3GPP        network. An HSS can perform functions of configuration storage,        identity management, user state storage, and so on.    -   RAN Application Part (RANAP): an interface between the RAN and a        node in charge of controlling a core network (in other words, a        Mobility Management Entity (MME)/Serving GPRS (General Packet        Radio Service) Supporting Node (SGSN)/Mobile Switching Center        (MSC)).    -   Public Land Mobile Network (PLMN): a network formed to provide        mobile communication services to individuals. The PLMN can be        formed separately for each operator.    -   Non-Access Stratum (NAS): a functional layer for exchanging        signals and traffic messages between a terminal and a core        network at the UMTS and EPS protocol stack. The NAS is used        primarily for supporting mobility of a terminal and a session        management procedure for establishing and maintaining an IP        connection between the terminal and a PDN GW.    -   Service Capability Exposure Function (SCEF): an entity in 3GPP        architecture for the service capability exposure that provides a        means for safely exposing a service and a capability provided by        3GPP network interface.    -   MME (Mobility Management Entity): A network node in an EPS        network, which performs mobility management and session        management functions    -   PDN-GW (Packet Data Network Gateway): A network node in the EPS        network, which performs UE IP address allocation, packet        screening and filtering, and charging data collection functions.    -   Serving GW (Serving Gateway): A network node in the EPS network,        which performs functions such as mobility anchor, packet        routing, idle mode packet buffering, and triggering paging for        the ME of MME    -   Policy and Charging Rule Function (PCRF): A node in the EPS        network, which performs policy decision to dynamically apply        differentiated QoS and billing policies for each service flow    -   Open Mobile Alliance Device Management (OMA DM): A protocol        designed to manage mobile devices such as mobile phones, PDAs,        and portable computers, which performs such functions as device        configuration, firmware upgrade, and error report    -   Operation Administration and Maintenance (OAM): A network        management function group which provides network fault        indication, performance information, and data and diagnostic        functions    -   NAS configuration MO (Management Object): A Management Object        (MO) used to configure the UE with the parameters associated        with the NAS functionality.    -   PDN (Packet Data Network): A network in which a server        supporting a specific service (e.g., MMS server, WAP server,        etc.) is located.    -   PDN connection: A connection from the UE to the PDN, that is,        the association (connection) between the UE represented by the        IP address and the PDN represented by the APN.    -   APN (Access Point Name): A string that refers to or identifies        the PDN. It is a name (string) (e.g.,        internet.mnc012.mcc345.gprs) predefined in the network when the        P-GW is accessed to access the requested service or network        (PDN).    -   Home Location Register (HLR)/Home Subscriber Server (HSS): A        database (DB) that represents subscriber information in the 3GPP        network.    -   NAS (Non-Access-Stratum): The upper stratum of the control plane        between the UE and the MME. It supports mobility management,        session management and IP address maintenance between the UE and        the network.    -   AS (Access-Stratum): It includes the protocol stack between the        UE and the radio (or access) network and is responsible for        transmitting data and network control signals.

In what follows, the present invention will be described based on theterms defined above.

Overview of system to which the present invention can be applied

FIG. 1 illustrates an Evolved Packet System (EPS) to which the presentinvention can be applied.

The network structure of FIG. 1 is a simplified diagram restructuredfrom an Evolved Packet System (EPS) including Evolved Packet Core (EPC).

The EPC is a main component of the System Architecture Evolution (SAE)intended for improving performance of the 3GPP technologies. SAE is aresearch project for determining a network structure supporting mobilitybetween multiple heterogeneous networks. For example, SAE is intended toprovide an optimized packet-based system which supports various IP-basedwireless access technologies, provides much more improved datatransmission capability, and so on.

More specifically, the EPC is the core network of an IP-based mobilecommunication system for the 3GPP LTE system and capable of supportingpacket-based real-time and non-real time services. In the existingmobile communication systems (namely, in the 2nd or 3rd mobilecommunication system), functions of the core network have beenimplemented through two separate sub-domains: a Circuit-Switched (CS)sub-domain for voice and a Packet-Switched (PS) sub-domain for data.However, in the 3GPP LTE system, an evolution from the 3rd mobilecommunication system, the CS and PS sub-domains have been unified into asingle IP domain. In other words, in the 3GPP LTE system, connectionbetween UEs having IP capabilities can be established through anIP-based base station (for example, eNodeB), EPC, and application domain(for example, IMS). In other words, the EPC provides the architectureessential for implementing end-to-end IP services.

The EPC comprises various components, where FIG. 1 illustrates part ofthe EPC components, including a Serving Gateway (SGW or S-GW), PacketData Network Gateway (PDN GW or PGW or P-GW), Mobility Management Entity(MME), Serving GPRS Supporting Node (SGSN), and enhanced Packet DataGateway (ePDG).

The SGW operates as a boundary point between the Radio Access Network(RAN) and the core network and maintains a data path between the eNodeBand the PDN GW. Also, in case the UE moves across serving areas by theeNodeB, the SGW acts as an anchor point for local mobility. In otherwords, packets can be routed through the SGW to ensure mobility withinthe E-UTRAN (Evolved-UMTS (Universal Mobile Telecommunications System)Terrestrial Radio Access Network defined for the subsequent versions ofthe 3GPP release 8). Also, the SGW may act as an anchor point formobility between the E-UTRAN and other 3GPP networks (the RAN definedbefore the 3GPP release 8, for example, UTRAN or GERAN (GSM (GlobalSystem for Mobile Communication)/EDGE (Enhanced Data rates for GlobalEvolution) Radio Access Network).

The PDN GW corresponds to a termination point of a data interface to apacket data network. The PDN GW can support policy enforcement features,packet filtering, charging support, and so on. Also, the PDN GW can actas an anchor point for mobility management between the 3GPP network andnon-3GPP networks (for example, an unreliable network such as theInterworking Wireless Local Area Network (I-WLAN) or reliable networkssuch as the Code Division Multiple Access (CDMA) network and Wimax).

In the example of a network structure as shown in FIG. 1, the SGW andthe PDN GW are treated as separate gateways; however, the two gatewayscan be implemented according to single gateway configuration option.

The MME performs signaling for the UE's access to the network,supporting allocation, tracking, paging, roaming, handover of networkresources, and so on; and control functions. The MME controls controlplane functions related to subscribers and session management. The MMEmanages a plurality of eNodeBs and performs signaling of theconventional gateway's selection for handover to other 2G/3G networks.Also, the MME performs such functions as security procedures,terminal-to-network session handling, idle terminal location management,and so on.

The SGSN deals with all kinds of packet data including the packet datafor mobility management and authentication of the user with respect toother 3GPP networks (for example, the GPRS network).

The ePDG acts as a security node with respect to an unreliable, non-3GPPnetwork (for example, I-WLAN, WiFi hotspot, and so on).

As described with respect to FIG. 1, a UE with the IP capability canaccess the IP service network (for example, the IMS) that a serviceprovider (namely, an operator) provides, via various components withinthe EPC based not only on the 3GPP access but also on the non-3GPPaccess.

Also, FIG. 1 illustrates various reference points (for example, S1-U,S1-MME, and so on). The 3GPP system defines a reference point as aconceptual link which connects two functions defined in disparatefunctional entities of the E-UTAN and the EPC. Table 1 below summarizesreference points shown in FIG. 1. In addition to the examples of FIG. 1,various other reference points can be defined according to networkstructures.

TABLE 1 Reference point Description S1-MME Reference point for thecontrol plane protocol between E-UTRAN and MME S1-U Reference pointbetween E-UTRAN and Serving GW for the per bearer user plane tunnelingand inter eNodeB path switching during handover S3 It enables user andbearer information exchange for inter 3GPP access network mobility inidle and/or active state. This reference point can be used intra-PLMN orinter-PLMN (e.g. in the case of Inter-PLMN HO). S4 It provides relatedcontrol and mobility support between GPRS core and the 3GPP anchorfunction of Serving GW. In addition, if direct tunnel is notestablished, it provides the user plane tunneling. S5 It provides userplane tunneling and tunnel management between Serving GW and PDN GW. Itis used for Serving GW relocation due to UE mobility if the Serving GWneeds to connect to a non-collocated PDN GW for the required PDNconnectivity. S11 Reference point for the control plane protocol betweenMME and SGW SGi It is the reference point between the PDN GW and thepacket data network. Packet data network may be an operator externalpublic or private packet data network or an intra-operator packet datanetwork (e.g., for provision of IMS services). This reference pointcorresponds to Gi for 3GPP accesses.

Among the reference points shown in FIG. 1, S2a and S2b corresponds tonon-3GPP interfaces. S2a is a reference point which provides reliable,non-3GPP access, related control between PDN GWs, and mobility resourcesto the user plane. S2b is a reference point which provides relatedcontrol and mobility resources to the user plane between ePDG and PDNGW.

FIG. 2 illustrates one example of an Evolved Universal Terrestrial RadioAccess Network (E-UTRAN) to which the present invention can be applied.

The E-UTRAN system has evolved from an existing UTRAN system and may bethe 3GPP LTE/LTE-A system, for example. A communication system isdisposed over a wide area to provide various communication servicesincluding voice communication through IMS and packet data (for example,VoIP (Voice over Internet Protocol)).

Referring to FIG. 2, an E-UMTS network comprises an E-UTRAN, EPC, andone or more UEs. The E-UTRAN comprises eNBs providing a UE with acontrol plane and user plane protocols, where the eNBs are connected toeach other through X2 interface.

The X2 user plane interface (X2-U) is defined among the eNBs. The X2-Uinterface provides non-guaranteed delivery of the user plane Packet DataUnit (PDU). The X2 control plane interface (X2-CP) is defined betweentwo neighboring eNBs. The X2-CP performs the functions of contextdelivery between eNBs, control of user plane tunnel between a source eNBand a target eNB, delivery of handover-related messages, uplink loadmanagement, and so on.

The eNB is connected to the UE through a radio interface and isconnected to the Evolved Packet Core (EPC) through the S1 interface.

The S1 user plane interface (S1-U) is defined between the eNB and theServing Gateway (S-GW). The S1 control plane interface (S1-MME) isdefined between the eNB and the Mobility Management Entity (MME). The S1interface performs the functions of EPS bearer service management, NASsignaling transport, network sharing, MME load balancing management, andso on. The S1 interface supports many-to-many-relation between the eNBand the MME/S-GW.

An MME is capable of performing various functions such as NAS signalingsecurity, AS (Access Stratum) security control, inter-CN (Core Network)signaling for supporting mobility among 3GPP access networks, IDLE modeUE reachability (including performing and controlling retransmission ofa paging message), TM (Tracking Area Identity) management (for IDLE andactive mode UEs), PDN GW and SGW selection, MME selection for handoverin which MMEs are changed, SGSN selection for handover to a 2G or 3G3GPP access network, roaming, authentication, bearer management functionincluding dedicated bearer establishment, and support for transmissionof a PWS (Public Warning System) (including Earthquake and TsunamiWarning System (ETWS) and Commercial Mobile Alert System (CMAS))message.

FIG. 3 illustrates structures of an E-UTRAN and an EPC in a wirelesscommunication system to which the present invention may be applied.

Referring to FIG. 3, an eNB is capable of performing functions such asselection of a gateway (for example, MME), routing to a gateway duringRRC (Radio Resource Control) activation, scheduling and transmission ofa BCH (Broadcast Channel), dynamic resource allocation for a UE inuplink and downlink transmission, and mobility control connection in anLTE ACTIVE state. As described above, a gateway belonging to an EPC iscapable of performing functions such as paging origination, LTE IDLEstate management, ciphering of a user plane, SAE (System ArchitectureEvolution) bearer control, and ciphering of NAS signaling and integrityprotection.

FIG. 4 illustrates a radio interface protocol structure between a UE andan E-UTRAN in a wireless communication system to which the presentinvention can be applied.

FIG. 4(a) illustrates a radio protocol structure for the control plane,and FIG. 4(b) illustrates a radio protocol structure for the user plane.

With reference to FIG. 4, layers of the radio interface protocol betweenthe UE and the E-UTRAN can be divided into a first layer (L1), a secondlayer (L2), and a third layer (L3) based on the lower three layers ofthe Open System Interconnection (OSI) model, widely known in thetechnical field of communication systems. The radio interface protocolbetween the UE and the E-UTRAN consists of the physical layer, data linklayer, and network layer in the horizontal direction, while in thevertical direction, the radio interface protocol consists of the userplane, which is a protocol stack for delivery of data information, andthe control plane, which is a protocol stack for delivery of controlsignals.

The control plane acts as a path through which control messages used forthe UE and the network to manage calls are transmitted. The user planerefers to the path through which the data generated in the applicationlayer, for example, voice data, Internet packet data, and so on aretransmitted. In what follows, described will be each layer of thecontrol and the user plane of the radio protocol.

The physical layer (PHY), which is the first layer (L1), providesinformation transfer service to upper layers by using a physicalchannel. The physical layer is connected to the Medium Access Control(MAC) layer located at the upper level through a transport channelthrough which data are transmitted between the MAC layer and thephysical layer. Transport channels are classified according to how andwith which features data are transmitted through the radio interface.And data are transmitted through the physical channel between differentphysical layers and between the physical layer of a transmitter and thephysical layer of a receiver. The physical layer is modulated accordingto the Orthogonal Frequency Division Multiplexing (OFDM) scheme andemploys time and frequency as radio resources.

A few physical control channels are used in the physical layer. ThePhysical Downlink Control Channel (PDCCH) informs the UE of resourceallocation of the Paging Channel (PCH) and the Downlink Shared Channel(DL-SCH); and Hybrid Automatic Repeat reQuest (HARQ) information relatedto the Uplink Shared Channel (UL-SCH). Also, the PDCCH can carry a ULgrant used for informing the UE of resource allocation of uplinktransmission. The Physical Control Format Indicator Channel (PCFICH)informs the UE of the number of OFDM symbols used by PDCCHs and istransmitted at each subframe. The Physical HARQ Indicator Channel(PHICH) carries a HARQ ACK (ACKnowledge)/NACK (Non-ACKnowledge) signalin response to uplink transmission. The Physical Uplink Control Channel(PUCCH) carries uplink control information such as HARQ ACK/NACK withrespect to downlink transmission, scheduling request, Channel QualityIndicator (CQI), and so on. The Physical Uplink Shared Channel (PUSCH)carries the UL-SCH.

The MAC layer of the second layer (L2) provides a service to the RadioLink Control (RLC) layer, which is an upper layer thereof, through alogical channel. Also, the MAC layer provides a function of mappingbetween a logical channel and a transport channel; andmultiplexing/demultiplexing a MAC Service Data Unit (SDU) belonging tothe logical channel to the transport block, which is provided to aphysical channel on the transport channel.

The RLC layer of the second layer (L2) supports reliable datatransmission. The function of the RLC layer includes concatenation,segmentation, reassembly of the RLC SDU, and so on. To satisfy varyingQuality of Service (QoS) requested by a Radio Bearer (RB), the RLC layerprovides three operation modes: Transparent Mode (TM), UnacknowledgedMode (UM), and Acknowledge Mode (AM). The AM RLC provides errorcorrection through Automatic Repeat reQuest (ARQ). Meanwhile, in casethe MAC layer performs the RLC function, the RLC layer can beincorporated into the MAC layer as a functional block.

The Packet Data Convergence Protocol (PDCP) layer of the second layer(L2) performs the function of delivering, header compression, cipheringof user data in the user plane, and so on. Header compression refers tothe function of reducing the size of the Internet Protocol (IP) packetheader which is relatively large and includes unnecessary control toefficiently transmit IP packets such as the IPv4 (Internet Protocolversion 4) or IPv6 (Internet Protocol version 6) packets through a radiointerface with narrow bandwidth. The function of the PDCP layer in thecontrol plane includes delivering control plane data andciphering/integrity protection.

The Radio Resource Control (RRC) layer in the lowest part of the thirdlayer (L3) is defined only in the control plane. The RRC layer performsthe role of controlling radio resources between the UE and the network.To this purpose, the UE and the network exchange RRC messages throughthe RRC layer. The RRC layer controls a logical channel, transportchannel, and physical channel with respect to configuration,re-configuration, and release of radio bearers. A radio bearer refers toa logical path that the second layer (L2) provides for data transmissionbetween the UE and the network. Configuring a radio bearer indicatesthat characteristics of a radio protocol layer and channel are definedto provide specific services; and each individual parameter andoperating methods thereof are determined. Radio bearers can be dividedinto Signaling Radio Bearers (SRBs) and Data RBs (DRBs). An SRB is usedas a path for transmitting an RRC message in the control plane, while aDRB is used as a path for transmitting user data in the user plane.

The Non-Access Stratum (NAS) layer in the upper of the RRC layerperforms the function of session management, mobility management, and soon.

A cell constituting the base station is set to one of 1.25, 2.5, 5, 10,and 20 MHz bandwidth, providing downlink or uplink transmission servicesto a plurality of UEs. Different cells can be set to differentbandwidths.

Downlink transport channels transmitting data from a network to a UEinclude a Broadcast Channel (BCH) transmitting system information, PCHtransmitting paging messages, DL-SCH transmitting user traffic orcontrol messages, and so on. Traffic or a control message of a downlinkmulti-cast or broadcast service can be transmitted through the DL-SCH orthrough a separate downlink Multicast Channel (MCH). Meanwhile, uplinktransport channels transmitting data from a UE to a network include aRandom Access Channel (RACH) transmitting the initial control messageand a Uplink Shared Channel (UL-SCH) transmitting user traffic orcontrol messages.

A logical channel lies above a transmission channel and is mapped to thetransmission channel. The logical channel may be divided into a controlchannel for delivering control area information and a traffic channelfor delivering user area information. The control channel may include aBCCH (Broadcast Control Channel), PCCH (Paging Control Channel), CCCH(Common Control Channel), DCCH (Dedicated Control Channel), and MCCH(Multicast Control Channel). The traffic channel may include a DTCH(Dedicated Traffic Channel) and MTCH (Multicast Traffic Channel). ThePCCH is a downlink channel for delivering paging information and is usedwhen a network does not know the cell to which a UE belongs. The CCCH isused by a UE that does not have an RRC connection to a network. The MCCHis a point-to-multipoint downlink channel used for delivering MBMS(Multimedia Broadcast and Multicast Service) control information from anetwork to a UE. The DCCH is a point-to-point bi-directional channelused by a UE with an RRC connection delivering dedicated controlinformation between a UE and a network. The DTCH is a point-to-pointchannel dedicated to one UE for delivering user information that mayexist in an uplink and downlink. The MTCH is a point-to-multipointdownlink channel for delivering traffic data from a network to a UE.

In the case of an uplink connection between a logical channel and atransport channel, the DCCH may be mapped to a UL-SCH, and the DTCH maybe mapped to a UL-SCH, and the CCCH may be mapped to a UL-SCH. In thecase of a downlink connection between a logical channel and a transportchannel, the BCCH may be mapped to a BCH or DL-SCH, the PCCH may bemapped to a PCH, the DCCH may be mapped to a DL-SCH, the DTCH may bemapped to a DL-SCH, the MCCH may be mapped to an MCH, and the MTCH maybe mapped to the MCH.

FIG. 5 illustrates an S1 interface protocol structure in a wirelesscommunication system to which the present invention can be applied.

FIG. 5(a) illustrates the control plane protocol stack in the S1interface, and FIG. 5(b) illustrates the user plane interface protocolstructure in the S1 interface.

With reference to FIG. 5, the S1 control plane interface (S1-MME) isdefined between the eNB and the MME. Similar to the user plane, thetransport network layer is based on IP transmission. However, to ensurereliable transmission of message signaling, the transport network layeris added to the Stream Control Transmission Protocol (SCTP) layer whichsits on top of the IP layer. The application layer signaling protocol iscalled S1 Application Protocol (S1-AP).

The SCTP layer provides guaranteed delivery of application layermessages.

The transport IP layer employs point-to-point transmission for ProtocolData Unit (PDU) signaling transmission.

For each S1-MME interface instance, single SCTP association uses a pairof stream identifiers for the S-MME common procedure. Only part ofstream identifier pairs is used for the S1-MME dedicated procedure. TheMME communication context identifier is allocated by the MME for theS1-MME dedicated procedure, and the eNB communication context identifieris allocated by the eNB for the S1-MME dedicated procedure. The MMEcommunication context identifier and the eNB communication contextidentifier are used for identifying a UE-specific S1-MME signalingtransmission bearer. The communication context identifier is deliveredwithin each S1-AP message.

In case the S1 signaling transport layer notifies the S1AP layer ofdisconnection of signaling, the MME changes the state of the UE whichhas used the corresponding signaling connection to ECM-IDLE state. Andthe eNB releases RRC connection of the corresponding UE.

The S1 user plane interface (S1-U) is defined between eNB and S-GW. TheS1-U interface provides non-guaranteed delivery of the user plane PDUbetween the eNB and the S-GW. The transport network layer is based on IPtransmission, and the GPRS Tunneling Protocol User Plane (GTP-U) layeris used on top of the UDP/IP layer to deliver the user plane PDU betweenthe eNB and the S-GW.

FIG. 6 illustrates a physical channel structure in a wirelesscommunication system to which the present invention may be applied.

Referring to FIG. 6, a physical channel delivers signaling and data byusing a radio resource comprising one or more subcarriers in thefrequency domain and one or more symbols in the time domain.

One subframe having a length of 1.0 ms comprises a plurality of symbols.A specific symbol(s) of a subframe (for example, a first symbol of asubframe) may be used for a PDCCH. The PDCCH carries information aboutdynamically allocated resources (for example, resource block and MCS(Modulation and Coding Scheme)).

EMM and ECM State

In what follows, EPS Mobility Management (EMM) and EPS ConnectionManagement (ECM) states will be described.

FIG. 7 illustrates an EMM and ECM states in a wireless communicationsystem to which the present invention can be applied.

With reference to FIG. 7, to manage mobility of the UE in the NAS layerdefined in the control planes of the UE and the MME, EMM-REGISTERED andEMM-DEREGISTERED states can be defined according to the UE is attachedto or detached from a network. The EMM-REGISTERED and theEMM-DEREGISTERED states can be applied to the UE and the MME.

Initially, the UE stays in the EMM-DEREGISTERED state as when the UE isfirst powered on and performs registering to a network through aninitial attach procedure to connect to the network. If the connectionprocedure is performed successfully, the UE and the MME makes transitionto the EMM-REGISTERED state. Also, in case the UE is powered off or theUE fails to establish a radio link (namely, a packet error rate for aradio link exceeds a reference value), the UE is detached from thenetwork and makes a transition to the EMM-DEREGISTERED state.

In addition, to manage signaling connection between the UE and thenetwork, ECM-CONNECTED and ECM-IDLE states can be defined. TheECM-CONNECTED and ECM-IDLE states can also be applied to the UE and theMME. ECM connection consists of RRC connection formed between the UE andthe eNB; and S1 signaling connection formed between the eNB and the MME.In other words, establishing/releasing an ECM connection indicates thatboth of the RRC connection and S1 signaling connection have beenestablished/released.

The RRC state indicates whether the RRC layer of the UE is logicallyconnected to the RRC layer of the eNB. In other words, in case the RRClayer of the UE is connected to the RRC layer of the eNB, the UE staysin the RRC CONNECTED state. If the RRC layer of the UE is not connectedto the RRC layer of the eNB, the UE stays in the RRC IDLE state.

The network can identify the UE staying in the ECM-CONNECTED state atthe level of cell unit and can control the UE in an effective manner.

On the other hand, the network is unable to know the existence of the UEstaying in the ECM-IDLE state, and a Core Network (CN) manages the UE onthe basis of a tracking area unit which is an area unit larger than thecell. While the UE stays in the ECM-IDLE state, the UE performsDiscontinuous Reception (DRX) that the NAS has configured by using theID allocated uniquely in the tracking area. In other words, the UE canreceive a broadcast signal of system information and paging informationby monitoring a paging signal at a specific paging occasion for eachUE-specific paging DRX cycle.

When the UE is in the ECM-IDLE state, the network does not carry contextinformation of the UE. Therefore, the UE staying in the ECM-IDLE statecan perform a mobility-related procedure based on the UE such as cellselection or cell reselection without necessarily following an order ofthe network. In case the location of the UE differs from the locationrecognized by the network while the UE is in the ECM-IDLE state, the UEcan inform the network of the corresponding location of the UE through aTracking Area Update (TAU) procedure.

On the other hand, when the UE is in the ECM-CONNECTED state, mobilityof the UE is managed by an order of the network. While the UE stays inthe ECM-CONNECTED state, the network knows to which cell the UEcurrently belongs. Therefore, the network can transit and/or receiverdata to or from the UE, control mobility of the UE such as handover, andperform cell measurement with respect to neighboring cells.

As described above, the UE has to make a transition to the ECM-CONNECTEDstate in order to receive a general mobile communication service such asa voice or data communication service. As when the UE is first poweredon, the UE in its initial state stays in the ECM-IDLE state as in theEMM state, and if the UE successfully registers to the correspondingnetwork through an initial attach procedure, the UE and the MEE make atransition to the ECM connection state. Also, in case the UE has alreadyregistered to the network but radio resources are not allocated astraffic is not activated, the UE stays in the ECM-IDLE state, and if newuplink or downlink traffic is generated for the corresponding UE, the UEand the MME make a transition to the ECM-CONNECTED state through aService Request procedure.

Random Access Procedure

In what follows, a random access procedure provided by the LTE/LTE-Asystem will be described.

A UE employs the random access procedure to obtain uplinksynchronization with an eNB or to have uplink radio resources. Afterbeing powered up, the UE acquires downlink synchronization with aninitial cell and receives system information. From the systeminformation, the UE obtains a set of available random access preamblesand information about a radio resource used for transmission of a randomaccess preamble. The radio resource used for transmission of a randomaccess preamble may be specified by a combination of at least one ormore subframe indices and indices on the frequency domain. The UEtransmits a random access preamble selected in a random fashion from theset of random access preambles, and the eNB receiving the random accesspreamble transmits a TA (Timing Alignment) value for uplinksynchronization through a random access response. By using the procedureabove, the UE obtains uplink synchronization.

The random access procedure is common to FDD (Frequency Division Duplex)and TDD (Time Division Duplex) scheme. The random access procedure isindependent of a cell size and is also independent of the number ofserving cells in case CA (Carrier Aggregation) is configured.

First, a UE performs the random access procedure in the following cases.

-   -   The case in which a UE performs initial access in an RRC idle        state in the absence of an RRC connection to an eNB    -   The case in which a UE performs an RRC connection        re-establishment procedure    -   The case in which a UE connects to a target cell for the first        time while performing a handover procedure    -   The case in which a random access procedure is requested by a        command from an eNB    -   The case in which downlink data are generated while uplink        synchronization is not met in the RRC connected state    -   The case in which uplink data are generated while uplink        synchronization is not met in the RRC connected state or a        designated radio resource used for requesting a radio resource        is not allocated    -   The case in which positioning of a UE is performed while timing        advance is needed in the RRC connected state    -   The case in which a recovery process is performed at the time of        a radio link failure or handover failure

The 3GPP Rel-10 specification takes into account applying a TA (TimingAdvance) value applicable to one specific cell (for example, P cell)commonly to a plurality of cells in a wireless access system. However, aUE may combine a plurality of cells belonging to different frequencybands (namely separated with a large distance in the frequency domain)or a plurality of cells having different propagation characteristics.Also, in the case of a specific cell, if the UE performs communicationwith the eNB (namely macro eNB) through one cell and performscommunication with the SeNB through other cell while a small cell suchas an RRH (Remote Radio Header) (namely repeater), femto-cell, orpico-cell or a secondary eNB (SeNB) is disposed within the cell forcoverage expansion or removal of a coverage hole, a plurality of cellsmay have different propagation delays. In this case, when the UEperforms uplink transmission so that one TA value is applied commonly toa plurality of cells, synchronization of uplink signals transmittedamong the plurality of cells may be seriously influenced. Therefore, itmay be preferable to have multiple TA values under the CA mode in whicha plurality of cells are aggregated. The 3GPP Rel-11 specification takesinto account allocating a TA value separately for each specific cellgroup to support multiple TA values. This is called a TA group (TAG); aTAG may have one or more cells, and the same TA value may be appliedcommonly to one or more cells belonging to the TAG. To support themultiple TA values, a MAC TA command control element is composed of a2-bit TAG Identity (ID) and a 6-bit TA command field.

The UE on which a carrier aggregation is configured performs the randomaccess procedure in case that the random access procedure previouslydescribed is required in connection with PCell. In case of TAG (that is,primary TAG (pTAG)) to which PCell belongs, the TA, which is determinedbased on PCell same as the existing case, or regulated through therandom access procedure that accompanies PCell, can be applied to allthe cells within the pTAG. Meanwhile, in case of TAG (that is, secondaryTAG (sTAG)) that is configured with SCells only, the TA, which isdetermined based on a specific SCell within sTAG, can be applied to allthe cells within the corresponding sTAG, and in this time, the TA may beacquired through the random access procedure by being initiated by theeNB. Particularly, the SCell in the sTAG is set to be a (Random AccessChannel) RACH resource, and the eNB requests a RACH access in SCell fordetermining TA. That is, the eNB initiates the RACH transmission on theSCells by PDCCH order that is transmitted from PCell. The responsemessage for the SCell preamble is transmitted through PCell by usingRA-RNTI. The TA that is determined based on SCell that successfullycompletes the random access can be applied to all the cells in thecorresponding sTAG by the UE. Like this, the random access procedure maybe performed in SCell as well in order to acquire timing alignment ofthe sTAG to which the corresponding SCell belongs.

In a process of selecting a random access preamble (RACH preamble), theLTE/LTE-A system supports both of a contention based random accessprocedure and a non-contention based random access procedure. In theformer procedure, a UE selects one arbitrary preamble from a specificset, while, in the latter procedure, the UE uses the random accesspreamble that an eNB has allocated only to the specific UE. It should benoted, however, that the non-contention based random access proceduremay be confined to the handover process described above, a caserequested by a command from the eNB, and UE positioning and/or timingadvance alignment for sTAG. After the random access procedure iscompleted, a normal uplink/downlink transmission occurs.

Meanwhile, a relay node (RN) also support both of the contention basedrandom access procedure and the non-contention based random accessprocedure. When a relay node performs the random access procedure, RNsubframe configuration is suspended. That is, this means that the RNsubframe configuration is temporarily discarded. Thereafter, the RNsubframe structure is resumed at the time when the random accessprocedure is successfully completed.

FIG. 8 illustrates a contention-based random access procedure in awireless communication system to which the present invention may beapplied.

(1) Msg 1 (Message 1)

First, a UE selects one random access preamble (RACH preamble) randomlyfrom a set of random access preambles indicated by system information ora handover command. The UE then selects a PRACH (Physical RACH) resourcecapable of transmitting the random access preamble and transmits therandom access preamble by using the PRACH resource.

A random access preamble is transmitted in six bits on the RACHtransmission channel, where the six bit comprises a 5-bit randomidentity for identifying a UE which transmits a RACH preamble and 1 bitfor representing additional information (for example, indicating size ofMsg 3).

An eNB which has received a random access preamble from a UE decodes thepreamble and obtains RA-RNTI. A time-frequency resource of a randomaccess preamble transmitted by the corresponding UE determines theRA-RNTI related to a PRACH to which a random access preamble istransmitted.

(2) Msg 2 (Message 2)

The eNB transmits a random access response to the UE, where the RA-RNTIobtained by using the preamble on Msg 1 addresses the random accessresponse. A random access response may include an RA preambleindex/identifier, UL grant indicating a uplink radio resource, TemporaryCell RNTI (TC-RNTI), and Time Alignment Command (TAC). A TAC indicates atime synchronization value that the eNB transmits to the UE to maintainuplink time alignment. The UE updates uplink transmission timing byusing the time synchronization value. If the UE updates timesynchronization, the UE initiates or restarts a time alignment timer.The UL grant includes uplink resource allocation and TPC (Transmit PowerCommand) used for transmitting a scheduling message (Msg 3) describedlater. The TPC is used to determine the transmission power for ascheduled PUSCH.

The UE attempts to receive a random access response within a randomaccess response window indicated by the eNB through system informationor a handover command, detects a PDCCH masked with an RA-RNTIcorresponding to the PRACH, and receives a PDSCH indicated by thedetected PDCCH. The random access response information may betransmitted in the form of a MAC PDU (MAC Packet Data Unit) and the MACPDU may be transmit through the PDSCH. It is preferable that the PDCCHshould include information of the UE that has to receive the PDSCH,frequency and time information of a radio resource of the PDSCH, andtransmission format of the PDSCH. As described above, once the UEsucceeds to detect the PDCCH transmitted to itself, it may properlyreceive a random access response transmitted to the PDSCH according tothe information of the PDCCH.

The random access response window refers to a maximum time interval inwhich the UE transmitting a preamble waits to receive a random accessresponse message. The random access response window has a length of‘ra-ResponseWindowSize’ starting from a subframe after three subframesin the last subframe transmitting a preamble. In other words, the UEwaits to receive a random access response during a random access windowsecured after three subframes from the subframe completed transmissionof the preamble. The UE may obtain the random access window size(‘ra-ResponseWindowsize’) parameter through system information, and therandom access window size is determined to be a value between 2 to 10.

If receiving a random access response having the same random accesspreamble delimiter/identity as that of the random access preambletransmitted to the eNB, the UE stops monitoring the random accessresponse. On the other hand, if failing to receive a random accessresponse message until a random access response window is terminated orfailing to receive a valid random access response having the same randomaccess preamble identity as that of the random access preambletransmitted to the eNB, the UE may consider reception of the randomaccess response as having failed and then perform retransmission of thepreamble.

As described above, the reason why a random access preamble identity isneeded for a random access response is that one random access responsemay include random access response information for one or more UEs andthus it is necessary to indicate to which UE the UL grant, TC-RNTI, andTAC is valid.

(3) Msg 3 (Message 3)

Receiving a valid random access response, the UE separately processesthe information included in the random access response. In other words,the UE applies the TAC and stores the TC-RNTI. Also, by using the ULgrant, the UE transmits the data stored in its buffer or newly generateddata to the eNB. In case the UE is connected for the first time, an RRCConnection request generated at the RRC layer and transmitted through aCCCH may be included in the Msg 3 and transmitted. And in the case of anRRC Connection Re-establishment procedure, an RRC ConnectionRe-establishment request generated at the RRC layer and transmittedthrough the CCCH may be included in the Msg 3 and transmitted. Also, aNAS connection request message may be included in the Msg 3.

The Msg 3 has to include a UE identity. In the case of a contentionbased random access procedure, the eNB is unable to determine which UEsperform the random access procedure. Thus, the eNB needs the UE identityfor each UE to avoid potential contention.

There are two methods for including UE identities. In the first method,if the UE already has a valid cell identity (C-RNTI) allocated by thecorresponding cell before performing the random access procedure, the UEtransmits its cell identity though a uplink transmission signalcorresponding to the UL grant. On the other hand, if the UE has notreceived a valid cell identity before performing the random accessprocedure, the UE transmits its unique identity (for example,S(SAE)-TMSI or a random number). In most cases, the unique identity islonger than the C-RNTI.

The UE uses UE-specific scrambling for transmission on UL-SCH. In casethe UE has received a C-RNTI, the UE may perform scrambling by using theC-RNTI. In case the UE has not received a C-RNTI yet, the UE is unableto perform C-RNTI based scrambling but uses a TC-RNTI received from arandom access response instead. If having received data corresponding tothe UL grant, the UE initiates a contention resolution timer forresolving contention.

(4) Msg 4 (Message 4)

Receiving the C-RNTI of a UE through the Msg 3 from the correspondingUE, the eNB transmits aMsg 4 to the UE by using the receiving C-RNTI. Onthe other hand, in case the eNB receives the unique identity (namelyS-TMSI or a random number) through the Msg 3, the eNB transmit the Msg 4to the UE by using a TC-RNTI allocated to the corresponding UE from arandom access response. As one example, the Msg 4 may include an RRCConnection Setup message.

After transmitting data including an identity through a UL grantincluded in the random access response, the UE waits for a command fromthe eNB to resolve contention. In other words, two methods are availablefor a method for receiving the PDCCH, too. As described above, in casethe identity in the Msg 3 transmitted in response to the UL grant is theC-RNTI, the UE attempts to receive the PDCCH by using its C-RNTI. Incase the identity is a unique identity (in other words, S-TMSI or arandom number), the UE attempts to receive the PDCCH by using theTC-RNTI included in the random access response. Afterwards, in theformer case, if the UE receives the PDCCH though its C-RNTI before thecontention resolution timer expires, the UE determines that the randomaccess procedure has been performed normally and terminates the randomaccess procedure. In the latter case, if the UE receives the PDCCHthrough the TC-RNTI before the contention resolution timer is completed,the UE checks the data transmitted by the PDSCH indicated by the PDCCH.If the data includes a unique identity of the UE, the UE determines thatthe random access procedure has been performed successfully andterminates the random access procedure. The UE obtains the C-RNTIthrough the Msg 4, after which the UE and the network transmit andreceive a UE dedicated message by using the C-RNTI.

Next, a method for resolving contention during random access will bedescribed.

The reason why contention occurs during random access is that the numberof random access preambles is, in principle, finite. In other words,since the eNB is unable to assign random access preambles unique to therespective UEs, a UE selects and transmits one from among common randomaccess preambles. Accordingly, although there are cases where two ormore UEs select and transmit the same random access preamble by usingthe same radio resource (PRACH resource), the eNB considers the randomaccess preamble as the one transmitted from a single UE. Thus, the eNBtransmits a random access response to the UE and expects that only oneUE receive the random access response. However, as described above,because of the possibility of contention, two or more UEs receive thesame random access response, and each receiving UE performs an operationdue to the random access response. In other words, a problem occurswhere two or more UEs transmit different data to the same radio resourceby using one UL grant included in the random access response.Accordingly, transmission of the data may all fail, or the eNB maysucceed to receive only the data from a specific UE depending on thepositions of transmission power of UEs. In the latter case, since two ormore UEs assume that they all have succeeded to transmit their data, theeNB has to inform those UEs that have failed in the contention abouttheir failure. In other words, contention resolution refers to theoperation of informing a UE about whether it has succeeded or failed.

Two methods are used for contention resolution. One of the methodsemploys a contention resolution timer and the other method employstransmitting an identity of a successful UE to other UEs. The formercase is used when a UE already has a unique C-RNTI before performing arandom access process. In other words, a UE that already has a C-RNTItransmits data including its C-RNTI to the eNB according to a randomaccess response and operates a contention resolution timer. And if theUE receives a PDCCH indicated by its C-RNTI before the contentionresolution timer expires, the UE determines that it has won thecontention and finishes random access normally. On the other hand, ifthe UE fails to receive a PDCCH indicated by its C-RNTI before thecontention resolution timer expires, the UE determines that it has lostthe contention and performs the random access process again or inform aupper layer of the failure. The latter contention resolution method,namely the method for transmitting an identity of a successful UE, isused when a UE does not have a unique cell identity before performingthe random access process. In other words, in case the UE has no cellidentity, the UE transmits data by including an upper identity (S-TMSIor a random number) higher than a cell identity in the data according tothe UL grant information included in a random access response andoperates a contention resolution timer. In case the data including theupper identity of the UE is transmitted to a DL-SCH before thecontention resolution timer expires, the UE determines that the randomaccess process has been performed successfully. On the other hand, incase the data including the upper identity of the UE is not transmittedto the DL-SCH before the contention resolution data expires, the UEdetermines that the random access process has failed.

Meanwhile, different from the contention based random access processillustrated in FIG. 11, a non-contention based random access processfinishes its procedures only by transmitting the Msg 1 and 2. However,before the UE transmits a random access preamble to the eNB as the Msg1, the eNB allocates a random access preamble to the UE. The randomaccess procedure is terminated as the UE transmits the allocated randomaccess preamble to the eNB as the Msg 1 and receives a random accessresponse from the eNB.

5G system architecture to which the present invention may be applied

A 5G system is a technology advanced from the 4th generation LTE mobilecommunication technology and a new radio access technology (RAT) throughthe evolution of the existing mobile communication network structure ora clean-state structure and an extended technology of long termevolution (LTE), and it supports extended LTE (eLTE), non-3GPP (e.g.,WLAN) access and so on.

A 5G system is defined based on a service, and an interaction betweennetwork functions (NFs) within architecture for a 5G system may beexpressed by two methods as follows.

-   -   Reference point representation (FIG. 9): indicates an        interaction between NF services within NFs described by a        point-to-point reference point (e.g., N11) between two NFs        (e.g., AMF and SMF).    -   Service-based representation (FIG. 10): network functions (e.g.,        AMFs) within a control plane (CP) permit other authenticated        network functions to access its own service. If this        representation is necessary, it also includes a point-to-point        reference point.

FIG. 9 is a diagram illustrating 5G system architecture using areference point representation.

Referring to FIG. 9, the 5G system architecture may include variouselements (i.e., a network function (NF)). This drawing illustrates anauthentication server function (AUSF), a (core) access and mobilitymanagement function (AMF), a session management function (SMF), a policycontrol function (PCF), an application function (AF), united datamanagement (UDM), a data network (DN), a user plane function (UPF), a(radio) access network ((R)AN) and a user equipment (UE) correspondingto some of the various elements.

Each of the NFs supports the following functions.

-   -   AUSF stores data for the authentication of a UE.    -   AMF provides a function for access of a UE unit and mobility        management and may be basically connected to one AMF per one UE.

Specifically, the AMF supports functions, such as signaling between CNnodes for mobility between 3GPP access networks, the termination of aradio access network (RAN) CP interface (i.e., N2 interface), thetermination (N1) of NAS signaling, NAS signaling security (NAS cipheringand integrity protection), AS security control, registration areamanagement, connection management, idle mode UE reachability (includingcontrol and execution of paging retransmission), mobility managementcontrol (subscription and policy), intra-system mobility andinter-system mobility support, the support of network slicing, SMFselection, lawful interception (for an AMF event and an interface to anLI system), the provision of transfer of a session management (SM)message between a UE and an SMF, a transparent proxy for SM messagerouting, access authentication, access authorization including a roamingright check, the provision of transfer of an SMS message between a UEand an SMSF(SMS(Short Message Service) function), a security anchorfunction (SEA) and/or security context management (SCM).

Some or all of the functions of the AMF may be supported within a singleinstance of one AMF.

-   -   DN means an operator service, Internet access or a 3rd party        service, for example. The DN transmits a downlink protocol data        unit (PDU) to an UPF or receives a PDU, transmitted by a UE,        from a UPF.    -   PCF provides a function for receiving information about a packet        flow from an application server and determining a policy, such        as mobility management and session management. Specifically, the        PCF supports functions, such as the support of a unified policy        framework for controlling a network behavior, the provision of a        policy rule so that a CP function(s) (e.g., AMF or SMF) can        execute a policy rule, and the implementation of a front end for        accessing related subscription information in order to determine        a policy within user data repository (UDR).    -   SMF provides a session management function and may be managed by        a different SMF for each session if a UE has a plurality of        sessions.

Specifically, the SMF supports functions, such as session management(e.g., session setup, modification and release including the maintenanceof a tunnel between a UPF and an AN node), UE IP address allocation andmanagement (optionally including authentication), the selection andcontrol of the UP function, a traffic steering configuration for routingtraffic from the UPF to a proper destination, the termination of aninterface toward policy control functions, the execution of the controlpart of a policy and QoS, lawful interception (for an SM event and aninterface to an LI system), the termination of the SM part of an NASmessage, downlink data notification, the initiator of AN-specific SMinformation (transferred to an AN through N2 via the AMF), thedetermination of an SSC mode of a session, and a roaming function.

Some or all of the functions of the SMF may be supported within a singleinstance of one SMF.

-   -   UDM stores the subscription data of a user, policy data, etc.        UDM includes two parts, that is, an application front end (FE)        and user data repository (UDR).

The FE includes a UDM FE responsible for the processing of locationmanagement, subscription management and credential and a PCF responsiblefor policy control. The UDR stores data required for functions providedby the UDM-FE and a policy profile required by the PCF. Data storedwithin the UDR includes user subscription data, including a subscriptionID, security credential, access and mobility-related subscription dataand session-related subscription data, and policy data. The UDM-FEsupports functions, such as access to subscription information stored inthe UDR, authentication credential processing, user identificationhandling, access authentication, registration/mobility management,subscription management, and SMS management.

-   -   UPF transfers a downlink PDU, received from a DN, to a UE via an        (R)AN and transfers an uplink PDU, received from a UE, to a DN        via an (R)AN.

Specifically, the UPF supports functions, such as an anchor point forintra/inter RAT mobility, the external PDU session point ofinterconnection to a data network, packet routing and forwarding, a userplane part for the execution of packet inspection and a policy rule,lawful interception, a traffic usage report, an uplink classifier forsupporting the routing of traffic flow of a data network, a branchingpoint for supporting a multi-home PDU session, QoS handling (e.g., theexecution of packet filtering, gating and an uplink/downlink rate) for auser plane, uplink traffic verification (SDF mapping between a servicedata flow (SDF) and a QoS flow), transport level packet marking withinthe uplink and downlink, downlink packet buffering, and a downlink datanotification triggering function. Some or all of the functions of theUPF may be supported within a single instance of one UPF.

-   -   AF interoperates with a 3GPP core network in order to provide        services (e.g., support functions, such as an application        influence on traffic routing, network capability exposure        access, an interaction with a policy framework for policy        control).    -   (R)AN collectively refers to a new radio access network        supporting all of evolved E-UTRA (E-UTRA) and new radio (NR)        access technologies (e.g., gNB), that is, an advanced version of        the 4G radio access technology.

The network node in charge of transmission/reception of wireless signalswith the UE is the gNB, and plays the same role as the eNB.

The gNB supports functions for radio resource management (i.e., radiobearer control and radio admission control), connection mobilitycontrol, the dynamic allocation (i.e., scheduling) of resources to a UEin the uplink/downlink, Internet protocol (IP) header compression, theencryption and integrity protection of a user data stream, the selectionof an AMF upon attachment of a UE if routing to the AMF has not beendetermined based on information provided to the UE, the selection of anAMF upon attachment of a UE, user plane data routing to an UPF(s),control plane information routing to an AMF, connection setup andrelease, the scheduling and transmission of a paging message (generatedfrom an AMF), the scheduling and transmission of system broadcastinformation (generated from an AMF or operation and maintenance (O&M)),a measurement and measurement report configuration for mobility andscheduling, transport level packet marking in the uplink, sessionmanagement, the support of network slicing, QoS flow management andmapping to a data radio bearer, the support of a UE that is an inactivemode, the distribution function of an NAS message, an NAS node selectionfunction, radio access network sharing, dual connectivity, and tightinterworking between an NR and an E-UTRA.

-   -   UE means a user device. A user apparatus may be called a term,        such as a terminal, a mobile equipment (ME) or a mobile station        (MS). Furthermore, the user apparatus may be a portable device,        such as a notebook, a mobile phone, a personal digital assistant        (PDA), a smartphone or a multimedia device, or may be a device        that cannot be carried, such as a personal computer (PC) or a        vehicle-mounted device.

In the drawings, for the clarity of description, an unstructured datastorage network function (UDSF), a structured data storage networkfunction (SDSF), a network exposure function (NEF) and an NF repositoryfunction (NRF) are not shown, but all of the NFs shown in this drawingmay perform mutual operations along with the UDSF, NEF and NRF, ifnecessary.

-   -   NEF provides means for safely exposing services and capabilities        provided by 3GPP network functions, for example, for a 3rd        party, internal exposure/re-exposure, an application function,        and edge computing. The NEF receives information from other        network function(s) (based on the exposed capability(s) of other        network function(s)). The NEF may store information received as        structured data using a standardized interface as a data storage        network function. The stored information is re-exposed to other        network function(s) and application function(s) by the NEF and        may be used for other purposes, such as analysis.    -   NRF supports a service discovery function. It receives an NF        discovery request from an NF instance and provides information        of a discovered NF instance to an NF instance. Furthermore, it        maintains available NF instances and services supported by the        available NF instances.    -   SDSF is an optional function for supporting a function of        storing and retrieving information as structured data by any        NEF.    -   UDSF is an optional function for supporting a function of        storing and retrieving information as unstructured data by any        NF.

In the 5G system, a node which is responsible for wirelesstransmission/reception with the UE is gNB and plays the same role as theeNB in the EPS. When the UE is simultaneously connected to the 3GPPconnection and the non-3GPP connection, the UE receives a servicethrough one AMF as illustrated in FIG. 9. In FIG. 9, it is illustratedthat a connection is made by the non-3GPP connection and a connection ismade by the 3GPP connection are connected to one same UPF, but theconnection is not particularly required and may be connected by aplurality of different UPFs.

However, when the UE selects N3IWK (also referred to as non-3GPPinterworking function (N3IWF)) in the HPLMN in the roaming scenario andis connected to the non-3GPP connection, the AMF that manages the 3GPPconnection may be located in the VPLMN and the AMF that manages thenon-3GPP connection may be located in the HPLMN.

The non-3GPP access network is connected to the 5G core network viaN3IWK/N3IWF. The N3IWK/N3IWF interfaces the 5G core network controlplane function and user plane function via the N2 and N3 interfaces,respectively.

A representative example of the non-3GPP connection mentioned in thepresent specification may be a WLAN connection.

Meanwhile, this drawing illustrates a reference model if a UE accessesone DN using one PDU session, for convenience of description, but thepresent invention is not limited thereto.

A UE may access two (i.e., local and central) data networks at the sametime using multiple PDU sessions. In this case, for different PDUsessions, two SMFs may be selected. In this case, each SMF may have theability to control both a local UPF and central UPF within a PDUsession, which can be independently activated per PDU.

Furthermore, a UE may access two (i.e., local and central) data networksprovided within one PDU session at the same time.

In the 3GPP system, a conceptual link that connects NFs within the 5Gsystem is defined as a reference point. The following illustratesreference points included in 5G system architecture represented in thisdrawing.

-   -   N1: a reference point between a UE and an AMF    -   N2: a reference point between an (R)AN and an AMF    -   N3: a reference point between an (R)AN and a UPF    -   N4: a reference point between an SMF and a UPF    -   N5: a reference point between a PCF and an AF    -   N6: a reference point between a UPF and a data network    -   N7: a reference point between an SMF and a PCF    -   N24: a reference point between a PCF within a visited network        and a PCF within a home network    -   N8: a reference point between a UDM and an AMF    -   N9: a reference point between two core UPFs    -   N10: a reference point between a UDM and an SMF    -   N11: a reference point between an AMF and an SMF    -   N12: a reference point between an AMF and an AUSF    -   N13: a reference point between a UDM and an authentication        server function (AUSF)    -   N14: a reference point between two AMFs    -   N15: a reference point between a PCF and an AMF in the case of a        non-roaming scenario and a reference point between a PCF within        a visited network and an AMF in the case of a roaming scenario    -   N16: a reference point between two SMFs (in the case of a        roaming scenario, a reference point between an SMF within a        visited network and an SMF within a home network)    -   N17: a reference point between an AMF and an EIR    -   N18: a reference point between any NF and an UDSF    -   N19: a reference point between an NEF and an SDSF

FIG. 10 is a diagram illustrating 5G system architecture using aservice-based representation.

A service-based interface illustrated in this drawing shows a set ofservices provided/exposed by a specific NF. The service-based interfaceis used within a control plane. The following illustrates service-basedinterfaces included in the 5G system architecture represented as in thisdrawing.

-   -   Namf: a service-based interface exhibited by an AMF    -   Nsmf: a service-based interface exhibited by an SMF    -   Nnef: a service-based interface exhibited by an NEF    -   Npcf: a service-based interface exhibited by a PCF    -   Nudm: a service-based interface exhibited by a UDM    -   Naf: a service-based interface exhibited by an AF    -   Nnrf: a service-based interface exhibited by an NRF    -   Nausf: a service-based interface exhibited by an AUSF

NF service is a kind of capability exposed to another NF (i.e., NFservice consumer) by an NF (i.e., NF service supplier) through aservice-based interface. The NF may expose one or more NF service(s). Inorder to define NF service, the following criteria are applied:

-   -   NF services are derived from an information flow for describing        an end-to-end function.    -   A complete end-to-end message flow is described by the sequence        of NF service invocation.    -   Two operations for NF(s) to provide their services through        service-based interfaces are as follows:

i) “Request-response”: a control plane NF_B (i.e., NF service supplier)receives a request to provide a specific NF service (including theexecution of an operation and/or the provision of information) fromanother control plane NF_A (i.e., NF service consumer). NF_B sends NFservice results based on information provided by NF_A within a requestas a response.

In order to satisfy a request, NF_B may alternately consume NF servicesfrom other NF(s). In the request-response mechanism, communication isperformed in a one-to-one manner between two NFs (i.e., consumer andsupplier).

ii) “subscribe-notify”

A control plane NF_A (i.e., NF service consumer) subscribes to an NFservice provided by another control plane NF_B (i.e., NF servicesupplier). A plurality of control plane NF(s) may subscribe to the samecontrol plane NF service. NF_B notifies interested NF(s) that havesubscribed to NF services of the results of the NF services. Asubscription request from a consumer may include a notification requestfor notification triggered through periodical update or a specific event(e.g., the change, specific threshold arrival, etc. of requestedinformation). The mechanism also includes a case where NF(s) (e.g.,NF_B) implicitly subscribe to specific notification without an explicitsubscription request (e.g., due to a successful registration procedure).

FIG. 11 illustrates NG-RAN architecture to which the present inventionmay be applied.

Referring to FIG. 11, a new generation radio access network (NG-RAN)includes an NR NodeB (gNB)(s) and/or an eNodeB (eNB)(s) for providingthe termination of a user plane and control plane protocol toward a UE.

An Xn interface is connected between gNBs and between a gNB(s) and aneNB(s) connected to 5GC. The gNB(s) and the eNB(s) are also connected to5GC using an NG interface. More specifically, the gNB(s) and eNB(s) arealso connected to an AMF using an NG-C interface (i.e., N2 referencepoint), that is, a control plane interface between an NG-RAN and 5GC andare connected to a UPF using an NG-U interface (i.e., N3 referencepoint), that is, a user plane interface between an NG-RAN and 5GC.

Radio Protocol Architecture

FIG. 12 is a diagram illustrating a radio protocol stack to which thepresent invention may be applied. Specifically, FIG. 12(a) illustrates aradio interface user plane protocol stack between a UE and a gNB, andFIG. 12(b) illustrates a radio interface control plane protocol stackbetween the UE and the gNB.

A control plane means a passage through which control messages aretransmitted in order for a UE and a network to manage a call. A userplane means a passage through which data generated in an applicationlayer, for example, voice data or Internet packet data is transmitted.

Referring to FIG. 12(a), the user plane protocol stack may be dividedinto a first layer (Layer 1) (i.e., a physical layer (PHY) layer) and asecond layer (Layer 2).

Referring to FIG. 12(b), the control plane protocol stack may be dividedinto a first layer (i.e., a PHY layer), a second layer, a third layer(i.e., a radio resource control (RRC) layer) and a non-access stratum(NAS) layer.

The second layer is divided into a medium access control (MAC) sublayer,a radio link control (RLC) sublayer, a packet data convergence protocol(PDC) sublayer, and a service data adaptation protocol (SDAP) sublayer(in the case of a user plane).

Radio bearers are classified into two groups: a data radio bearer (DRB)for user plane data and a signaling radio bearer (SRB) for control planedata

Hereinafter, the layers of the control plane and user plane of the radioprotocol are described.

1) The PHY layer, that is, the first layer, provides informationtransfer service to a higher layer using a physical channel. The PHYlayer is connected to the MAC sublayer located in a high level through atransport channel. Data is transmitted between the MAC sublayer and thePHY layer through a transport channel. The transport channel isclassified depending on how data is transmitted according to whichcharacteristics through a radio interface. Furthermore, data istransmitted between different physical layers, that is, between the PHYlayer of a transmission stage and the PHY layer of a reception stagethrough a physical channel.

2) The MAC sublayer performs mapping between a logical channel and atransport channel; the multiplexing/demultiplexing of an MAC servicedata unit (SDU) belonging to one logical channel or different logicalchannels to/from a transport block (TB) transferred to/from the PHYlayer through a transport channel; a scheduling information report;error correction through a hybrid automatic repeat request (HARQ);priority handling between UEs using dynamic scheduling; priorityhandling between the logical channels of one UE using logical channelpriority; and padding.

Different types of data transfer service provided by the MAC sublayer.Each logical channel type defines that information of which type istransferred.

Logical channels are classified into two groups: a control channel and atraffic channel.

i) The control channel is used to transfer only control planeinformation and is as follows.

-   -   Broadcast control channel (BCCH): a downlink channel system for        broadcasting control information.    -   Paging control channel (PCCH): a downlink channel transferring        paging information and system information change notification.    -   Common control channel (CCCH): a channel for transmitting        control information between a UE and a network. This channel is        used for UEs not having an RRC connection with a network.    -   Dedicated control channel (DCCH): a point-to-point bidirectional        channel for transmitting dedicated control information between a        UE and a network. It is used by a UE having an RRC connection.

ii) The traffic channel is used to use only user plane information:

-   -   Dedicated traffic channel (DTCH): a point-to-point channel for        transferring user information and dedicated to a single UE. The        DTCH may be present in both the uplink and downlink.

In the downlink, a connection between a logical channel and a transportchannel is as follows.

A BCCH may be mapped to a BCH. A BCCH may be mapped to a DL-SCH. A PCCHmay be mapped to a PCH. A CCCH may be mapped to a DL-SCH. A DCCH may bemapped to a DL-SCH. A DTCH may be mapped to a DL-SCH.

In the uplink, a connection between a logical channel and a transportchannel is as follows. A CCCH may be mapped to an UL-SCH. A DCCH may bemapped to an UL-SCH. A DTCH may be mapped to an UL-SCH.

3) The RLC sublayer supports three transport modes: a transparent mode(TM), an unacknowledged mode (UM) and acknowledged mode (AM).

An RLC configuration may be applied to each logical channel. In the caseof an SRB, the TM or AM mode is used. In contrast, in the case of a DRB,the UM or AM mode is used.

The RLC sublayer performs the transfer a higher layer PDU; independentsequence numbering with a PDCP; error correction through an automaticrepeat request (ARW); segmentation and re-segmentation; the reassemblyof an SDU; RLC SDU discard; and RLC re-establishment.

4) The PDCP sublayer for a user plane performs sequence numbering;header compression and compression-decompression (corresponding to onlyrobust header compression (RoHC)); user data transfer; reordering andduplicate detection (if there is transfer to a layer higher than thePDCP); PDCP PDU routing (in the case of a split bearer); theretransmission of a PDCP SDU; ciphering and deciphering; PDCP SDUdiscard; PDCP re-establishment and data recovery for RLC AM; and theduplication of a PDCP PDU.

The PDCP sublayer a control plane additionally performs sequencenumbering; ciphering, deciphering and integrity protection; controlplane data transfer; duplication detection; the duplication of a PDCPPDU.

When duplication for a radio bearer is configured by RRC, an additionalRLC entity and an additional logical channel are added to a radio bearerin order to control a duplicated PDCP PDU(s). In the PDCP, duplicationincludes transmitting the same PDCP PDU(s) twice. The first one istransferred to the original RLC entity, and the second one istransferred to an additional RLC entity. In this case, the duplicationcorresponding to the original PDCP PDU is not transmitted to the sametransport block. Different two logical channels may belong to the sameMAC entity (in the case of a CA) or to different MAC entities (in thecase of DC). In the former case, a logical channel mapping restrictionis used to guarantee that a duplication corresponding to the originalPDCP PDU is not transferred to the same transport block.

5) The SDAP sublayer performs i) mapping between a QoS flow and a dataradio bearer and ii) QoS flow ID marking within a downlink and uplinkpacket.

One protocol entity of an SDAP is configured for each PDU session, butexceptionally in the case of dual connectivity (DC), two SDAP entitiesmay be configured.

6) The RRC sublayer performs the broadcasting of system informationrelated to an access stratum (AS) and a non-access stratum (NAS); paginginitiated by 5GC or an NG-RAN; the establishment, maintenance andrelease (additionally including the modification and release of acarrier aggregation and additionally including the modification andrelease of dual connectivity between an E-UTRAN and an NR or within anNR) of an RRC connection between a UE and an NG-RAN; a security functionincluding key management; the establishment, configuration, maintenanceand release of an SRB(s) and a DRB(s); handover and context transfer;control of UE cell selection, re-release and cell selection/reselection;a mobility function including mobility between RATs; a QoS managementfunction, a UE measurement report and report control; the detection of aradio link failure and recovery from a radio link failure; and thetransfer of an NAS message from an NAS to a UE and the transfer of anNAS message from a UE to an NAS.

FIG. 13 illustrates a protocol stack between a UE and a core network of5G/NR system to which the present invention is applicable.

N1 may play a role similar to a NAS protocol of EPS, and N2 may play arole similar to S1-AP of EPS. 5G RRC and 5G AS respectively correspondto existing LTE RRC and LTE AS, or NR RRC and NR AS of NR that are newlybeing standardized, and RRCs of all two RATs are excepted to be based oncurrent LTE RRC.

Network Slicing

A 5G system has introduced a network slicing technology which providesnetwork resources and network functions to an independent slice based oneach service.

As network slicing is introduced, the isolation, independent management,etc. of a network function and network resources can be provided foreach slice. Accordingly, services that are independent for each serviceor user and that are more flexible can be provided by selecting andcombining network functions of the 5G system depending on a service oruser.

A network slice refers to a network that logically integrates an accessnetwork and a core network.

The network slice may include one or more of the followings:

-   -   Core network control plane and user plane function    -   NG-RAN    -   Non-3GPP interworking function (N3IWF) toward a non-3GPP access        network

A function supported for each network slice and network functionoptimization may be different. A plurality of network slice instancesmay provide the same function to different groups of UEs.

One UE may be connected to one or more network slice instances at thesame time via a 5G-AN. One UE may be served at the same time by amaximum of 8 network slices. An AMF instance that serves a UE may belongto each network slice instance that serves the UE. That is, the AMFinstance may be common to a network slice instance that serves the UE.The CN part of a network slice instance(s) that serves a UE is selectedby a CN.

One PDU session belongs to only a specific one network slice instancefor each PLMN. Different network slice instances do not share one PDUsession.

One PDU session belongs to a specific one network slice instance foreach PLMN. Different slices may have slice-specific PDU sessions usingthe same DNN, but different network slice instances do not share one PDUsession.

Single network slice selection assistance information (S-NSSAI)identifies a network slice. Each S-NSSAI is assistant information usedfor a network to select a specific network slice instance. The NSSAI isa set of S-NSSAI(s). The S-NSSAI includes the followings:

-   -   Slice/service type (SST): the SST indicates the operation of a        network slice expected form a viewpoint of a function and        service.    -   Slice differentiator (SD): the SD is optional information that        supplements an SST(s) for selecting a network slice instance        from a plurality of potential network slice instances all of        which comply with an indicated SST.

1) Upon Initial Access, Network Slice Selection

A Configured NSSAI may be configured in a UE by a home PLMN (HPLMN) foreach PLMN. The Configured NSSAI becomes PLMN-specific, and the HPLMNindicates a PLMN(s) to which each Configured NSSAI has been applied.

Upon initial connection of a UE, an RAN selects an initial network slicethat will transfer a message using an NSSAI. To this end, in aregistration procedure, a UE provides a requested NSSAI to a network. Inthis case, when the UE provides the requested NSSAI to the network, a UEwithin a specific PLMN uses only S-NSSAIs belonging to the ConfiguredNSSAI of the corresponding PLMN.

If a UE does not provide an NSSAI to an RAN and an RAN does not select aproper network slice based on the provided NSSAI, the RAN may select adefault network slice.

Subscription data includes the S-NSSAI(s) of a network slice(s) to whicha UE has subscribed. One or more S-NSSAI(s) may be marked as a defaultS-NSSAI. When an S-NSSAI is marked by default, although a UE does nottransmit any S-NSSAI to a network within a Registration Request, thenetwork may serve the UE through a related network slice.

When a UE is successfully registered, a CN notifies an (R)AN of all ofAllowed NSSAIs (including one or more S-NSSAIs) by providing the NSSAIs.Furthermore, when the registration procedure of the UE is successfullycompleted, the UE may obtain an Allowed NSSAI for a PLMN from an AMF.

The Allowed NSSAI has precedence over the Configured NSSAI for the PLMN.Thereafter, the UE uses only an S-NSSAI(s) within the Allowed NSSAIcorresponding to a network slice for a network slice selection-relatedprocedure within the serving PLMN.

In each PLMN, a UE stores a Configured NSSAI and an Allowed NSSAI (ifpresent). When the UE receives an Allowed NSSAI for a PLMN, it overridesthe previously stored Allowed NSSAI for the PLMN.

2) Slice Change

A network may change an already selected network slice instancedepending on a local policy and the mobility, subscription informationchange, etc. of a UE. That is, a set of network slices of a UE may bechanged at any time while the UE is registered with a network.Furthermore, a change of a set of network slices of a UE may beinitiated by a network or under specific conditions.

A network may change a set of allowed network slice(s) with which a UEhas been registered based on a local policy, a subscription informationchange and/or the mobility of the UE. A network may perform such achange during a registration procedure or may notify a UE of a change ofa supported network slice(s) using a procedure capable of triggering aregistration procedure.

Upon changing the network slice, the network may provide the UE with anew Allowed NSSAI and a tracking area list. The UE includes the newNSSAI in signaling according to a mobility management procedure andtransmits the signaling, thereby causing the reselection of a sliceinstance. An AMF supporting the slice instance may also be changed inresponse to a change of the slice instance.

When a UE enters an area in which a network slice is no longeravailable, a core network releases a PDU session for an S-NSSAIcorresponding to a network slice that is no longer available through aPDU session release procedure.

When the PDU session corresponding to the slice that is no longeravailable is released, the UE determines whether the existing trafficcan be routed through a PDU session belonging to another slice using aUE policy.

For a change of a set of used S-NSSAI(s), a UE initiates a registrationprocedure.

3) SMF Selection

A PCF provides a UE with a network slice selection policy (NSSP). TheNSSP associates the UE with an S-NSSAI and is used by the UE in order todetermine a PDU session to which traffic will be routed.

A network slice selection policy is provided for each application of aUE. This includes a rule by which an S-NSSAI can be mapped for each UEapplication. The AMF selects an SMF for PDU session management usingsubscriber information and a local operator policy along with anSM-NSSAI transferred by a UE and DNN information.

When a PDU session for a specific slice instance is established, a CNprovides an (R)AN with an S-NSSAI corresponding to the slice instance towhich the PDU session belongs so that an RAN can access a specificfunction of a slice instance.

Session Management

5GC supports a PDU connectivity service, that is, a service thatprovides the exchange of PDU(s) between a UE and a DN identified by adata network name (DNN) (or an access point name (APN)). The PDUconnectivity service is also supported through a PDU session establishedupon request from the UE.

Each PDU session supports a single PDU session type. That is, when thePDU session is established, it supports the exchange of PDUs of a singletype requested by a UE. The following PDU session types are defined. IPversion 4 (IPv4), IP version 6 (IPv6), Ethernet, and unstructured. Inthis case, the type of PDUs exchanged between a UE and a DN arecompletely transparent in a 5G system.

A PDU session is established using NAS SM signaling exchanged between aUE and an SMF through N1 (upon UE request), modified (upon UE and 5GCrequest), and released (upon UE and 5GC request). Upon request from anapplication server, 5GC may trigger a specific application within a UE.When the UE receives a trigger message, it transfers the correspondingmessage to an identified application. The identified application mayestablish a PDU session with a specific DNN.

An SMF checks whether a UE request complies with user subscriptioninformation. To this end, the SMF obtains SMF level subscription datafrom UDM. Such data may indicate an accepted PDU session type for eachDNN:

A UE registered through a plurality of accesses selects access forsetting up a PDU session.

A UE may request to move a PDU session between 3GPP and non-3GPP access.A determination for moving the PDU session between 3GPP and non-3GPPaccess is made for each PDU session. That is, the UE may have a PDUsession using 3GPP access while another PDU session uses non-3GPPaccess.

Within a PDU session setup request transmitted by a network, a UEprovides a PDU session identity (ID). Furthermore, the UE may provide aPDU session type, slicing information, a DNN, service and a sessioncontinuity (SSC) mode.

A UE may establish a plurality of PDU sessions with the same DN ordifferent DNs at the same time via 3GPP access and/or via non-3GPPaccess.

A UE may establish a plurality of PDU sessions with the same DN servedby a different UPF end N6.

A UE having a plurality of established PDU sessions may be served bydifferent SMFs.

The user plane path of a different PDU sessions belonging to the same UE(the same or different DNNs) may be fully separated between an UPF andAN interfacing with a DN.

5G system architecture can satisfy various continuity requirements ofdifferent application/services within a UE by supporting a session andservice continuity (SCC). A 5G system supports different SSC modes. AnSSC mode associated with a PDU session anchor is not changed while a PDUsession is established.

-   -   In the case of a PDU session to which SSC Mode 1 is applied, a        network maintains continuity service provided to a UE. In the        case of a PDU session of an IP type, an IP address is        maintained.    -   If SSC Mode 2 is used, a network may release continuity service        delivered to a UE. Furthermore, the network may release a        corresponding PDU session. In the case of a PDU session of an IP        type, a network may release an IP address(s) allocated to a UE.    -   If SSC Mode 3 is used, a change of a user plane can be aware by        a UE, but a network guarantees that the UE does not lose        connectivity. In order to permit better service continuity, a        connection through a new PDU session anchor point is established        before a previous connection is terminated. In the case of a PDU        session of an IP type, an IP address is not maintained while an        anchor is deployed again.

An SSC mode selection policy is used to determine the type of SSC modeassociated with an application (or application group) of a UE. Anoperator may previously configure an SSC mode selection policy in a UE.The policy includes one or more SSC mode selection policy rules whichmay be used for a UE to determine the type of SSC mode associated withan application (or a group of applications). Furthermore, the policy mayinclude a default SSC mode selection policy rule which may be applied toall of applications of a UE.

If a UE provides an SSC mode when it requests a new PDU session, an SMFselects whether it will accept the requested SSC mode or whether it willmodify the requested SSC mode based on subscription information and/or alocal configuration. If a UE does not provide an SSC mode when itrequests a new PDU session, an SMF selects a default SSC mode for datanetworks listed within subscription information or applies a localconfiguration for selecting an SSC mode.

An SMF notifies a UE of an SSC mode selected for a PDU session.

Mobility Management

Registration management (RM) is used to register or deregister a UE/userwith/from a network and to establish user context within a network.

1) Registration Management

A UE/user needs to register a network in order to receive service thatrequests registration. Once the UE/user is registered, the UE may updateits own registration with the network in order to periodically maintainreachability (periodical registration update) if applicable, upon moving(mobility registration update), or in order to update its own capabilityor negotiate a protocol parameter again.

An initial registration procedure includes the execution of a networkaccess control function (i.e., user authentication and accessauthentication based on a subscription profile within UDM). As theresults of the registration procedure, the ID of a serving AMF withinthe UDM is registered.

FIG. 13 illustrates RM state models to which the present invention maybe applied. Specifically, FIG. 13(a) shows an RM state model within aUE, and FIG. 13(b) shows an RM state model within an AMF.

Referring to FIG. 13, in order to reflect the registration state of a UEwithin a selected PLMN, two RM states of RM-DEREGISTERED andRM-REGISTERED are used within the UE and the AMF.

In the RM-DEREGISTERED state, the UE is not registered with a network.The valid location or routing information of UE context within the AMFis not maintained. Accordingly, the UE is not reachable by the AMF.However, for example, in order to prevent an authentication procedurefrom being executed for each registration procedure, some UE context maybe still stored in the UE and the AMF.

In the RM-DEREGISTERED state, if the UE needs to receive service thatrequests registration, the UE attempts registration with a selected PLMNusing the initial registration procedure. Alternatively, upon initialregistration, when the UE receives a Registration Reject, the UE remainsin the RM-DEREGISTERED state. In contrast, when the UE receives theRegistration Accept, it enters the RM-REGISTERED state.

-   -   In the RM-DEREGISTERED state, if applicable, the AMF accepts the        initial registration of the UE by transmitting a Registration        Accept to the UE, and enters the RM-REGISTERED state.        Alternatively, if applicable, the AMF rejects the initial        registration of the UE by transmitting a Registration Reject to        the UE.

In the RM-REGISTERED state, the UE is registered with the network. Inthe RM-REGISTERED state, the UE may receive service that requestsregistration with the network.

-   -   In the RM-REGISTERED state, if the tracking area identity (TAI)        of a current serving cell is not present within a list of TAIs        that has been received by the UE from a network, the        registration of the UE is maintained. The UE performs a mobility        registration update procedure so that the AMF can page the UE.        Alternatively, in order to notify a network that the UE is still        in the active state, the UE performs a periodic registration        update procedure when a periodical update timer expires.        Alternatively, in order to update its own capability information        or negotiate a protocol parameter with a network again, the UE        performs a registration update procedure. Alternatively, if the        UE does no longer require registration with a PLMN, the UE        performs a deregistration procedure and enters the        RM-DEREGISTERED state. The UE may determine deregistration from        the network at any time. Alternatively, when the UE receives a        Registration Reject message, a Deregistration message or        performs a local deregistration procedure without the initiation        of any signaling, it enters the RM-DEREGISTERED state.    -   In the RM-REGISTERED state, when the UE does no longer need to        be registered with the PLMN, the AMF performs a deregistration        procedure and enters the RM-DEREGISTERED state. The AMF may        determine the deregistration of the UE at any time.        Alternatively, after an implicit deregistration timer expires,        the AMF performs implicit deregistration at any time. The AMF        enters the RM-DEREGISTERED state after the implicit        deregistration. Alternatively, the AMF performs local        deregistration for the UE that has negotiated deregistration at        the end of communication. The AMF enters the RM-DEREGISTERED        state after local deregistration. Alternatively, if applicable,        the AMF accepts or rejects registration update from the UE. The        AMF may reject UE registration when it rejects the registration        update from the UE.

Registration area management includes a function for allocating orre-allocating a registration area to the UE. The registration area ismanaged for each access type (i.e., 3GPP access or non-3GPP access).

When the UE is registered with a network through 3GPP access, the AMFallocates a set of tracking area (TA)(s) within a TAI list to the UE.When the AMF allocates a registration area (i.e., a set of TAs withinthe TAI list), the AMF may consider various types of information (e.g.,a mobility pattern and an accepted/non-accepted area). The AMP havingthe whole PLMN or all of PLMNs as a serving area may allocate the wholePLMN, that is, a registration area, to the UE in the MICO mode.

A 5G system supports the allocation of a TAI list including different5G-RAT(s) within a single TAI list.

When the UE is registered with a network through non-3GPP access, aregistration area for the non-3GPP access corresponds to a uniquereserved TAI value (i.e., dedicated to the non-3GPP access).Accordingly, there is a unique TA for the non-3GPP access to 5GC, whichis called an N3GPP TAI.

When the TAI list is generated, the AMF includes only a TAI(s)applicable to access through which the TAI list has been transmitted.

2) Connection Management

Connection management (CM) is used to establish and release a signalingconnection between the UE and the AMF. CM includes a function ofestablishing and releasing a signaling connection between the UE and theAMF through N1. The signaling connection is used to enable an NASsignaling exchange between the UE and a core network. The signalingconnection includes both an AN signaling connection for the UE betweenthe UE and the AN and an N2 connection for the UE between the AN and theAMF.

FIG. 14 illustrates CM state models to which the present invention maybe applied. Specifically, FIG. 14 (a) illustrates a CM state shiftwithin a UE, and FIG. 14 (b) shows a CM state shift within an AMF.

Referring to FIG. 14, in order to reflect the NAS signaling connectionof the UE with the AMF, two CM states of CM-IDLE and CM-CONNECTED areused.

The UE in the CM-IDLE state is the RM-REGISTERED state and does not havean NAS signaling connection established with the AMF through N1. The UEperforms cell selection, cell reselection and PLMN selection.

An AN signaling connection, an N2 connection and an N3 connection forthe UE in the CM-IDLE state are not present.

-   -   In the CM-IDLE state, if the UE is not in the MICO mode, it        responds to paging by performing a Service Request procedure (if        it has received it). Alternatively, when the UE has uplink        signaling or user data to be transmitted, it performs a Service        Request procedure. Alternatively, whenever an AN signaling        connection is established between the UE and the AN, the UE        enters the CM-CONNECTED state. Alternatively, the transmission        of an initial NAS message (Registration Request, Service Request        or Deregistration Request) starts to shift from the CM-IDLE        state to the CM-CONNECTED state.    -   In the CM-IDLE state, if the UE is not in the MICO mode, when        the AMF has signaling or the mobile-terminated data to be        transmitted to the UE, it performs a network-triggered service        request procedure by transmitting a paging request to the        corresponding UE. Whenever an N2 connection for a corresponding        UE between the AN and the AMF is established, the AMF enters the        CM-CONNECTED state.

The UE in the CM-CONNECTED state has an NAS signaling connection withthe AMF through N1.

In the CM-CONNECTED state, whenever the AN signaling connection isreleased, the UE enters the CM-IDLE state.

-   -   In the CM-CONNECTED state, whenever an N2 signaling connection        and N3 connection for the UE are released, the AMF enters the        CM-IDLE state.    -   When an NAS signaling procedure is completed, the AMF may        determine to release the NAS signaling connection of the UE.        When the AN signaling connection release is completed, the CM        state within the UE changes to the CM-IDLE. When an N2 context        release procedure is completed, the CM state for the UE within        the AMF changes to the CM-IDLE.

The AMF may maintain the UE in the CM-CONNECTED state until the UE isderegistered from a core network.

The UE in the CM-CONNECTED state may be an RRC Inactive state. When theUE is in the RRC Inactive state, UE reachability is managed by an RANusing assistant information from a core network. Furthermore, when theUE is in the RRC Inactive state, UE paging is managed by the RAN.Furthermore, when the UE is in the RRC Inactive state, the UE monitorspaging using the CN and RAN ID of the UE.

The RRC Inactive state is applied to an NG-RAN (i.e., applied to an NRand E-UTRA connected to 5G CN).

The AMF provides assistant information to the NG-RAN in order to assistthe determination of the NG-RAN regarding whether the UE will be changedto the RRC Inactive state based on a network configuration.

The RRC Inactive assistant information includes a UE-specificdiscontinuous reception (DRX) value for RAN paging during the RRCInactive state and a registration area provided to the UE.

CN assistant information is provided to a serving NG RAN node during N2activation (i.e., registration, a service request or path switch).

The state of an N2 and the N3 reference point is not changed by the UEthat enters the CM-CONNECTED state accompanied by RRC Inactive. The UEin the RRC Inactive state is aware of an RAN notification area.

When the UE is the CM-CONNECTED state accompanied by RRC Inactive, theUE may resume an RRC connection due to uplink data pending, amobile-initiated signaling procedure (i.e., periodical registrationupdate), a response to RAN paging, or when the UE notifies a networkthat it has deviated from the RAN notification area.

When the connection of the UE in a different NG-RAN node within the samePLMN resumes, UE AS context is recovered from an old NG RAN node, andthe procedure is triggered toward a CN.

When the UE is in the CM-CONNECTED state accompanied by RRC Inactive,the UE performs cell selection on a GERAN/UTRAN/EPS and complies with anidle mode procedure.

Furthermore, the UE in the CM-CONNECTED state accompanied by RRCInactive enters the CM-IDLE mode and complies with an NAS procedurerelated to the following cases.

-   -   If an RRC resumption procedure fails,    -   If a movement to the CM-IDLE mode of the UE is required within a        failure scenario that cannot be solved in the RRC Inactive mode.

The NAS signaling connection management includes a function forestablishing and releasing an NAS signaling connection.

The NAS signaling connection establishment function is provided by theUE and the AMF in order to establish the NAS signaling connection of theUE in the CM-IDLE state.

When the UE in the CM-IDLE state needs to transmit an NAS message, theUE initiates a service request or registration procedure in order toestablish a signaling connection to the AMF.

The AMF may maintain the NAS signaling connection until the UE isderegistered from a network based on the preference of the UE, UEsubscription information, a UE mobility pattern and a networkconfiguration.

The procedure of releasing the NAS signaling connection is initiated bya 5G (R)AN node or the AMF.

When the UE detects the release of an AN signaling connection, the UEdetermines that the NAS signaling connection has been released. When theAMF detects that N2 context has been released, the AMF determines thatthe NAS signaling connection has been released.

3) UE Mobility Restriction

A mobility restriction restricts the service access or mobility controlof a UE within a 5G system. A mobility restriction function is providedby a UE, an RAN and a core network.

The mobility restriction is applied to only 3GPP access, but is notapplied to non-3GPP access.

In the CM-IDLE state and the CM-CONNECTED state accompanied by RRCInactive, a mobility restriction is performed by a UE based oninformation received from a core network. In the CM-CONNECTED state, amobility restriction is performed by an RAN and a core network.

In the CM-CONNECTED state, a core network provides a handoverrestriction list for a mobility restriction to an RAN.

The mobility restriction includes an RAT restriction, a forbidden areaand a service area restriction as follows:

-   -   RAT restriction: the RAT restriction is defined as a 3GPP RAT(s)        whose access of a UE is not permitted. A UE within a restricted        RAT is not allowed to initiate any communication with a network        based on subscription information.    -   Forbidden area: a UE is not allowed to initiate any        communication with a network based on subscription information        within a forbidden area under a specific RAT.    -   Service area restriction: it defines an area in which a UE can        initiate cannot initiate communication with a network as        follows:    -   Allowed area: if a UE is allowed by subscription information        within an allowed area under a specific RAT, the UE is allowed        to initiate communication with a network.    -   Non-allowed area: a service area for a UE is restricted based on        subscription information within a non-allowed area under a        specific RAT. The UE and the network are not allowed to initiate        session management signaling for obtaining a service request or        user service (both the CM-IDLE state and the CM-CONNECTED        state). The RM procedure of the UE is the same as that in the        allowed area. A UE within a non-allowed area responds to the        paging of a core network as a service request.

In a specific UE, a core network determines a service area restrictionbased on UE subscription information. Optionally, an allowed area may befine-tuned by a PCF (e.g., based on a UE location, a permanent equipmentidentifier (PEI) or a network policy). The service area restriction maybe changed due to subscription information, a location, a PEI and/or apolicy change, for example. The service area restriction may be updatedduring a registration procedure.

If a UE has an RAT restriction, a forbidden area, an allowed area, anon-allowed area or an area overlapping between them, the UE performs anoperation according to the following priority:

-   -   The evaluation of the RAT restriction has precedence over the        evaluation of any other mobility restriction;    -   The evaluation of the forbidden area has precedence over the        evaluation of the allowed area and the non-allowed area; and    -   The evaluation of the non-allowed area has precedence over the        evaluation of the allowed area.

4) Mobile Initiated Connection Only (MICO) Mode

A UE may indicate the preference of the MICO mode during initialregistration or registration update. The AMF determines whether the MICOmode is permitted for the UE based on a local configuration, thepreference indicated by the UE, UE subscription information and anetwork policy or a combination of them, and notifies the UE of theresults during a registration procedure.

A UE and a core network re-initiates or exits from the MICO mode in thefollowing registration signaling. If the MICO mode is not clearlyindicated within a registration procedure and a registration procedureis successfully completed, the UE and the AMF do not use the MICO mode.That is, the UE operates as a general UE, and the network also treats acorresponding UE as a general UE.

The AMF allocates a registration area to a UE during a registrationprocedure. When the AMF indicates the MICO mode for the UE, theregistration area is not restricted as a paging area size. If the AMFserving area is the whole PLMN, the AMF may provide the UE with the“whole PLMN” registration area. In this case, re-registration with thesame PLMN attributable to mobility is not applied. If a mobilityrestriction is applied to a UE in the MICO mode, the AMF allocates anallowed area/non-allowed area to the UE.

When the AMF indicates the MICO mode for the UE, the AMF considers thatthe UE is always unreachable during the CM-IDLE state. The AMF rejectsany request for downlink data transfer for a corresponding UE that is inthe MICO mode and the CM-IDLE state. The AMF also delays downlinktransport, such as SMS or location service through the NAS. A UE in theMICO mode may be reachable for mobile-terminated data or signaling onlywhen the UE is in the CM-CONNECTED mode.

The AMF may provide an RAN node with pending data indication when a UEin the MICO mode can immediately transport mobile-terminated data and/orsignaling when the UE switches to the CM-CONNECTED mode. When the RANnode receives the indication, the RAN node considers the informationwhen it determines user inactivity.

A UE in the MICO mode does not need to listen to paging during theCM-IDLE state. The UE in the MICO mode may stop any AS procedure withinthe CM-IDLE state until it starts switching from the CM-IDLE to theCM-CONNECTED mode due to one of the following reasons.

-   -   If a change (e.g., configuration change) within the UE requires        registration update to a network    -   If a periodic registration timer expires    -   If MO data is pending    -   If MO(Mobile Originating) signaling is pending

Quality of Service (QoS) Model

QoS is a technology for the smooth transfer service of various traffic(mail, data transmission, audio and video) to a user depending on eachcharacter.

A 5G QoS model supports a framework-based QoS flow. The 5G QoS modelsupports both a QoS flow that requires a guaranteed flow bit rate (GFBR)and a QoS flow that does not require the GFBR.

The QoS flow is the finest granularity for QoS classification in a PDUsession.

A QoS flow ID (QFI) is used to identify a QoS flow within a 5G system.The QFI is unique within a PDU session. User plane traffic having thesame QFI within a PDU session receives the same traffic transferprocessing (e.g., scheduling and an admission threshold). The QFI istransferred within an encapsulation header on N3 (and N9). The QFI maybe applied to a different payload type of a PDU (i.e., an IP packet,unstructured packet and Ethernet frame).

In this specification, for convenience of description, “QoS” and a “QoSflow” are interchangeably used. Accordingly, in this specification,“QoS” may be construed as meaning a “QoS flow”, and “QoS” may beconstrued as meaning a “QoS flow.”

Within a 5G system, QoS flows may be controlled by an SMF upon PDUsession setup or QoS flow establishment/modification.

If applicable, all of QoS flows have the following characteristics:

-   -   QoS profile previously configured in the AN or provided from the        SMF to the AN via the AMF through the N2 reference point;    -   One or more networks provided from the SMF to the UE via the AMF        through the N1 reference point—provided QoS rule(s) and/or one        or more UE-derived QoS rule(s)    -   SDF classification provided from the SMF to the UPF through the        N4 reference point and QoS-related information (e.g.,        session-aggregate maximum bit rate (AMBR)).

The QoS flow may become a “guaranteed bit rate (GBR)” or a“non-guaranteed bit rate (non-GBR)” depending on the QoS profile. TheQoS profile of the QoS flow includes the following QoS parameters:

i) With respect to each of QoS flows, QoS parameters may include thefollowings:

-   -   5G QoS indicator (5QI): the 5QI is a scalar for referring to 5G        QoS characteristics (i.e., control QoS transfer handling access        node-specific parameters for a QoS flow, for example, scheduling        weight, an admission threshold, a queue management threshold and        a link layer protocol configuration).    -   Allocation and retention priority (APR): the ARP includes a        priority level, a pre-emption capability and pre-emption        vulnerability. The priority level defines the relative        importance of a resource request. This is used to determine        whether a new QoS flow will be accepted or rejected if resources        are restricted and to used to determine whether the existing QoS        flow will pre-empt resources while the resources are restricted.

ii) Furthermore, only in the case of each GBR QoS flow, QoS parametersmay further include the followings:

-   -   GFBR—the uplink and downlink;    -   Maximum flow bit rate (MFBR)—the uplink and downlink; and    -   Notification control.

iii) Only in the case of a non-GBR QoS flow, QoS parameters may furtherinclude the following: Reflective QoS attribute (RQA)

There are supported methods of controlling the following QoS flows:

1) In the case of the non-GBR QoS flow: if a standardized 5QI or apreviously configured 5QI is used, a 5QI value is used as the QFI of theQoS flow and a default ARP is previously configured in the AN;

2) In the case of the GBR QoS flow: if a standardized 5QI or apreviously configured 5QI is used, a 5QI value is used as the QFI of theQoS flow. A default ARP is transmitted to the RAN when a PDU session isestablished. Whenever the NG-RAN is used, the user plane (UP) of the PDUsession is activated;

3) In the case of the GBR and non-GBR QoS flow: an allocated QFI isused. A 5QI value may be standardized, previously configured or notstandardized. The QoS profile and QFI of the QoS flow may be provided tothe (R)AN through N2 when a PDU session is established or when a QoSflow is established/changed. Whenever the NG-RAN is used, the user plane(UP) of the PDU session is activated.

A UE may perform the marking and classification (i.e., the associationof UL traffic for a QoS flow) of UL user plane traffic based on a QoSrule. Such rules may be explicitly provided to the UE (when a PDUsession is established or a QoS flow is established) or may have beenpreviously configured in the UE or may be implicitly derived by the UEby applying reflective QoS.

The QoS rule may include a unique QoS rule ID within a PDU session, theQFI of an associated QoS flow, and one or more packet filters andprecedence value. Additionally, with respect to an allocated QFI, theQoS rule may include QoS parameters related to a UE. One or more QoSrules associated with the same QoS flow (i.e., having the same QFI) maybe present.

The default QoS rule may be necessary for all of PDU sessions. Thedefault QoS rule may be a unique QoS rule of a PDU session that may notinclude a packet filter (In this case, the highest precedence value(i.e., the lowest priority) should be used). If the default QoS ruledoes not include a packet filter, the default QoS rule defines theprocessing of packets not matched with another QoS rule in a PDUsession.

The SMF performs binding between SDFs for a QoS flow depending on theQoS of an SDF and service requirements. The SMF allocates a QFI to a newQoS flow, and derives the QoS parameter of the new QoS flow frominformation provided by the PCF. If applicable, the SMF may provide an(R)AN with a QFI along with a QoS profile. The SMF provides an SDFtemplate (i.e., a set of packet filters associated with the SDF receivedfrom the PCF) along with SDF priority, QoS-related information andcorresponding packet marking information (i.e., a QFI, a differentiatedservices code point (DSCP) value and optionally enables theclassification, bandwidth application and marking of user plane trafficusing reflective QoS indication for a UPF). If applicable, the SMFgenerates QoS rule(s) for a PDU session by allocating unique QoS ruleIDs within a PDU session to which the QFI of a QoS flow has been added,configuring packet filter(s) for the UL part of the SDF template, andsetting QoS rule priority in the SDF priority. The QoS rule is providedto a UE that enables the classification and marking of UL user planetraffic.

FIG. 15 illustrates classification and user plane marking for a QoS flowand the mapping of a QoS flow to AN resources according to an embodimentof the present invention.

1) Downlink

An SMF allocates a QFI for each QoS flow. Furthermore, the SMF derivesQoS parameters from information provided by a PCF.

The SMF provides an (R)AN with the QFI along with a QoS profileincluding the QoS parameters of a QoS flow. Furthermore, when a PDUsession or QoS flow is established, the QoS parameters of the QoS flowis provided to the (R)AN as the QoS profile through N2. Furthermore,whenever an NG-RAN is used, a user plane is activated. Furthermore, QoSparameters may be previously configured in the (R)AN for a non-GBR QoSflow.

Furthermore, the SMF provides an UPF with an SDF template (i.e., a setof packet filters associated with the SDF received from the PCF) alongwith SDF preference and a corresponding QFI so that the UPF can performthe classification and marking of a downlink user plane packet.

Downlink inflow data packets are classified based on the SDF templateaccording to the SDF preference (without the initiation of additional N4signaling). A CN classifies user plane traffic belonging to a QoS flowthrough N3 (and N9) user plane marking using the QFI. The AN binds theQoS flow with AN resources (i.e., a DRB in the case of the 3GPP RAN). Inthis case, a relation between the QoS flow and the AN resources is notrestricted to 1:1. The AN may configure the AN resources necessary tomap a QoS flow to a DRB so that a UE may receive the QFI (and reflectiveQoS may be applied).

If matching is not discovered, when all of QoS flows are related to oneor more DL packet filters, the UPF may discard a DL data packet.

Characteristics applied to process downlink traffic are as follows:

-   -   The UPF maps user plane traffic to the QoS flow based on the SDF        template.    -   The UPF performs session-AMBR execution and performs PDU        counting for charging support.    -   The UPF may transmit the PDUs of a PDU session in a single        tunnel between 5GC and the (A)AN, and the UPF may include the        QFI in an encapsulation header.    -   The UPF performs transmission level packet marking in the        downlink (e.g., sets DiffServ code in an outer IP header).        Transmission level packet marking is based on 5QI and the ARP of        an associated QoS flow.    -   The (R)AN maps PDUs from a QoS flow to access-specific resources        based on a QFI, related 5G QoS characteristics and parameters by        considering an N3 tunnel associated with a downlink packet.    -   If reflective QoS is applied, a UE may generate a new derived        QoS rule (or may be called a “UE-derived QoS rule”). A packet        filter within the derived QoS rule may be derived from a DL        packet (i.e., the header of the DL packet). The QFI of the        derived QoS rule may be configured depending on the QFI of the        DL packet.

2) Uplink

The SMF generates QoS rule(s) for a PDU session by allocating a QoS ruleID, adding the QFI of a QoS flow, setting packet filter(s) in the uplinkpart of an SDF template, and setting QoS rule precedence in SDFprecedence. The SMF may provide a UE with the QoS rules in order for theUE to perform classification and marking.

The QoS rule includes a QoS rule ID, the QFI of a QoS flow, one or morepacket filters and preference values. The same QFI (i.e., the same QoSflow) and one or more QoS rules may be associated.

A default QoS rule is required for each PDU session. The default QoSrule is the QoS rule of a PDU session not including a packet filter (Inthis case, the highest precedence value (i.e., the lowest priority) isused). If the default QoS rule does not include a packet filter, thedefault QoS rule defines the processing of a packet not matched with anyanother QoS rule within the PDU session.

The UE performs the classification and marking of uplink user planetraffic. That is, the UE associates uplink traffic with the QoS flowbased on the QoS rule. The rule may be explicitly signaled through N1(when a PDU session is established or when a QoS flow is established ormay be previously configured in the UE or may be implicitly derived bythe UE from reflected QoS.

In the UL, the UE evaluates an UL packet with respect to the packetfilter of the QoS rule based on the precedence value of the QoS rule(i.e., in order of increasing precedence value) until a matching QoSrule (i.e., the packet filter is matched with the UL packet) isdiscovered. The UE binds the UL packet to the QoS flow using a QFI inthe corresponding matching QoS rule. The UE binds the QoS flow and theAN resources.

If matching is not discovered and a default QoS rule includes one ormore UL packet filters, the UE may discard an UL data packet.

Characteristics applied to process uplink traffic are as follows:

-   -   A UE may use stored QoS rules in order to determine mapping        between UL user plane traffic and a QoS flow. The UE may mark an        UL PDU with the QFI of a QoS rule including a matching packet        filter, and may transmit the UL PDU using corresponding        access-specific resources for a QoS flow based on mapping        provided by an RAN.    -   The (R)AN transmits the PDU through an N3 tunnel with respect to        an UPF. When an UL packet passes through a CN from the (R)AN,        the (R)AN includes a QFI in the encapsulation header of the UL        PDU and selects the N3 tunnel.    -   The (R)AN may perform transmission level packet marking in the        uplink. The transmission level packet marking may be based on        the ARP of a QoS flow associated with a 5QI.    -   A UPF checks whether the QFIs of UL PDUs are provided to the UE        or are aligned (e.g., in the case of reflective QoS) with QoS        rules implicitly derived by the UE.    -   The UPF performs session-AMBF execution and counts a packet for        charging.

In the case of an UL classifier PDU session, UL and DL session-AMBRsneed to be performed on an UPF that supports an UL classifier function.Furthermore, the DL session-AMBR needs to be separately performed in allof UPFs that terminate an N6 interface (i.e., an interaction betweenUPFs is not required).

In the case of a multi-home PDU session, UL and DL session-AMBRs areapplied to an UPF that supports a branch point function. Furthermore,the DL session-AMBR needs to be separately performed in all of UPFs thatterminate the N6 interface (i.e., an interaction between UPFs is notrequired).

The (R)AN needs to perform a maximum bit rate (UE-AMBR) restriction inthe UL and DL for each non-GBR QoS flow. When the UE receives asession-AMBR, it needs to perform a PDU session-based UL raterestriction for non-GBR traffic using the session-AMBR. The raterestriction execution for each PDU session is applied to a flow thatdoes not require a guaranteed flow bit rate. The MBR per SDF ismandatory to a GBR QoS flow, but is optional for a non-GBR QoS flow. TheMBR is performed in the UPF.

QoS control for an unstructured PDU is performed in a PDU session level.When the PDU session is established for the transmission of theunstructured PDU, the SMF provides the UPF and the UE with a QFI to beapplied to any packet of the PDU session.

MM/SM Separation

In a core network of 5th generation system (5GS), a network node (AMF)managing a mobility and a network node (SMF) managing a session havebeen divided as separate functions. If MME has played a main role of acontrol plane in the existing EPC, etc., entity/node has beenmodularized and divided per main function in 5GC. That is, in the 5GS,it may be considered that the existing MME has been divided into an AMFresponsible for a mobility management function and a SMF responsible fora session management function.

The SMF managing each session is responsible for SM related NAS layermessage and procedure, and the AMF is responsible for an overallmobility management (MM) including a registration management (RM) and aconnection management (CM) of the UE itself. The roles of the AMF andthe SMF currently defined in TS 23.501 are as follows.

1. AMF

The AMF includes the following functionality. Some or all of the AMFfunctionalities may be supported in a single instance of the AMF:

-   -   Termination of RAN CP interface (N2)    -   Termination of NAS (N1), NAS ciphering and integrity protection    -   Registration management    -   Connection management    -   Reachability management    -   Mobility management    -   Lawful intercept (for AMF events and interface to LI System)    -   Transparent proxy for routing SM messages    -   Access authentication    -   Access authorization    -   Security Anchor Function (SEA): The SEA interacts with the AUSF        and the UE and receives an intermediate key that is established        as a result of the UE authentication process. In case of USIM        based authentication, the AMF retrieves the security material        from the AUSF.    -   Security Context Management (SCM): The SCM receives a key from        the SEA that it uses to derive access-network specific keys.

Regardless of the number of network functions, there is only one NASinterface instance per access network between the UE and the CN, andterminated at one of the Network functions that implements at least NASsecurity and mobility management.

In addition to the functionalities of the AMF described above, the AMFmay include the following functionality to support non-3GPP accessnetworks:

-   -   Support of N2 interface with N3IWF. Over this interface, some        information (e.g., 3GPP cell identification) and procedures        (e.g., hand-over related) defined over 3GPP access may not        apply, and non-3GPP access specific information may be applied        that do not apply to 3GPP accesses.    -   Support of NAS signaling with a UE over N3IWF. Some procedures        supported by NAS signaling over 3GPP access may be not        applicable to untrusted non-3GPP (e.g., paging) access.    -   Support of authentication of UEs connected over N3IWF.    -   Management of mobility and authentication/security context        state(s) of a UE connected via non-3GPP access or connected via        3GPP and non-3GPP accesses simultaneously.    -   Support of a coordinated RM management context valid over 3GPP        and non-3GPP accesses.    -   Support of dedicated CM management contexts for the UE for        connectivity over non-3GPP access.

Not all of the functionalities are required to be supported in aninstance of a network slice.

2. SMF

The session management function (SMF) includes the followingfunctionality. Some or all of the SMF functionalities may be supportedin a single instance of a SMF:

-   -   Session management (e.g., session establishment, modification,        and release, including tunnel maintenance between the UPF and an        AN node.    -   UE IP address allocation and management (including optional        authorization).    -   Selection and control of UP function.    -   Configuring traffic steering at UPF to route traffic to proper        destination.    -   Termination of interfaces towards policy control functions.    -   Controlling part of policy enforcement and QoS.    -   Lawful intercept (for SM events and interface to LI System).    -   Termination of SM parts of NAS messages.    -   Downlink data notification.    -   Initiator of AN specific SM information, sent via AMF over N2 to        AN.    -   Determining SSC mode of a session (for IP type PDU session)    -   Roaming functionality:    -   Handling local enforcement to apply QoS SLAB (VPLMN).    -   Charging data collection and charging interface (VPLMN).    -   Lawful intercept (in VPLMN for SM events and interface to LI        System).

Support for interaction with external DN for transport of signaling forPDU session authorization/authentication by external DN.

Not all of the functionalities are required to be supported in aninstance of a network slice.

In order to start a SM procedure, in the same manner as the existingprocedure, a CM-CONNECTED state, i.e., secure signaling connectionbetween the UE and the CN should be necessarily established. A SM NASmessage shall go through the AMF, but the SM NAS message is transparentto the AMF. That is, the AMF cannot decrypt or recognize the contents ofthe SM NAS message itself passing through the AMF. Thus, if there areseveral SMFs, the AMF needs to be separately instructed as to which SMFforwards/routes the NAS message. To this end, information for separateforwarding/routing may be added to the outside of the SM NAS message.

If a PDU session has been already created, a PDU session ID of thecorresponding PDU session may be represented in a part (particularly,outside the SM NAS message) that the AMF can decrypt, and the AMF canfind/recognize the SMF to forward/route the message based on this. Inthis instance, a mapping table scheme, etc. may be used. If a PDUsession is not created, the AMF may perform a SMF selection function inconsideration of information such as DNN and S-NSSAI, in order to selectan appropriate SMF. Information that is used for the AMF to select theappropriate SMF may be represented, by the UE, in the part that the AMFcan decrypt/recognize and may be provided to the AMF.

Registration Procedure

In 5GS, the existing Attach procedure and TAU procedure have beencombined and defined as a registration procedure. However, theregistration procedure may be divided into/called an initialregistration (Attach) procedure, a registration update (TAU) procedure,a periodic registration update (p-TAU) procedure, etc. depending on itspurpose.

Whether session establishment can be performed during the registrationprocedure is currently under discussion, and there may be a method forentering an SM procedure immediately after an RM procedure is ended, anda method for piggybacking and sending an SM message in the same manneras EPC technology.

A registration procedure currently reflected in TS 23.502 v0.2.0 is asthe following FIG. 17.

FIG. 17 is a flow chart illustrating a registration procedure applicableto the present invention.

1. UE to (R)AN: AN message (AN parameters, registration request(registration type, subscriber permanent identifier (SUPI) or temporaryuser ID, security parameters, NSSAI, UE 5GCN capability, PDU sessionstatus)).

In case of 5G-RAN, the AN parameters include, for example, the SUPI orthe temporary user ID, the selected network and/or NSSAI.

The registration type may indicate if the UE wants to perform an“initial registration (i.e. the UE is in a non-registered state)”, a“mobility registration update (i.e. the UE is in a registered state andinitiates a registration procedure due to mobility)” or a “periodicregistration update (i.e. the UE is in a registered state and initiatesa registration procedure due to the periodic update timer expiry)”. Ifincluded, the temporary user ID indicates the last serving AMF. If theUE is already registered via a non-3GPP access in a PLMN different fromthe PLMN of the 3GPP access, the UE shall not provide the UE temporaryID allocated by the AMF during the registration procedure over thenon-3GPP access.

The security parameters are used for authentication and integrityprotection. NSSAI indicates network slice selection assistanceinformation. The PDU session status indicates the available (previouslyestablished) PDU sessions in the UE.

2. If a SUPI is included or the temporary user ID does not indicate avalid AMF, the (R)AN, based on (R)AT and NSSAI, if available, selects anAMF. The (R)AN selects an AMF as described in TS 23.501. If the (R)ANcannot select an AMF, it forwards the registration request to a defaultAMF. The default AMF is responsible for selecting an appropriate AMF forthe UE. The relocation between the default AMF and the selected AMF isdescribed in clause 4.2.2.2.3, where the initial AMF refers to thedefault AMF, and the target AMF refers to the selected AMF.

3. (R)AN to AMF: N2 message (N2 parameters, registration request(registration type, subscriber permanent identifier or temporary userID, security parameters, NSSAI)).

When 5G-RAN is used, the N2 parameters include location information,cell identity and RAT type related to the cell in which the UE iscamping.

If the registration type indicated by the UE is periodic registrationupdate, the steps 4 to 17 may be omitted.

4. [conditional] new AMF to old AMF: Information Request (completeregistration request)

If the UE's temporary user ID is included in the registration requestand the serving AMF has changed since last registration, the new AMF maysend information request to old AMF including the complete registrationrequest IE to request the UE's SUPI and MM context.

5. [conditional] old AMF to new AMF: Information Response (SUPI, MMcontext, SMF information). The Old AMF responds with informationresponse to new AMF including the UE's SUPI and MM Context. If old AMFholds information about active PDU sessions, the old AMF includes SMFinformation including SMF identities and PDU session identities.

6. [conditional] AMF to UE: Identify Request ( ).

If the SUPI is not provided by the UE nor retrieved from the old AMF theidentity request procedure is initiated by AMF sending an identityrequest message to the UE.

7. [conditional] UE to AMF: Identify Request ( ).

The UE responds with an Identity response message including the SUPI.

8. The AMF may decide to invoke an AUSF. In this case, the AMF mayselect an AUSF based on SUPI.

9. The AUSF shall initiate authentication of the UE and NAS securityfunctions.

A procedure including AMF relocation (e.g., due to network slicing) mayhappen after step 9.

10. [conditional] new AMF to old AMF: Information Acknowledged ( ).

If the AMF has changed, the new AMF acknowledges the transfer of UE MMcontext. If the authentication/security procedure fails, theregistration is rejected, and the new AMF sends a reject indication tothe old AMF. The old AMF continues the procedure as if the informationrequest was never received.

11. [conditional] AMF to UE: Identity Request ( ).

If the PEI was not provided by the UE nor retrieved from the old AMF,the identity request procedure is initiated by sending, by the AMF, anidentity request message to the UE to retrieve the PEI.

12. Optionally, the AMF initiates ME identity. The PEI check isperformed as described in clause 4.7.

13. If step 14 is to be performed, the AMF selects a UDM based on theSUPI.

The AMF selects an UDM as described in TS 23.501.

14. If the AMF has changed since the last registration, or if there isno valid subscription context for the UE in the AMF, or if the UEprovides a SUPI which does not refer to a valid context in the AMF, theAMF can initiate an update location procedure. This includes that theUDM initiates cancel location to the old AMF, if any. The old AMFremoves the MM context and notifies all possibly associated SMF(s), andthe new AMF can create an MM context for the UE after getting the AMFrelated subscription data from the UDM. The update location procedure isperformed according to TS 23.501.

The PEI is provided to the UDM in the update location procedure.

15. Conditionally, the AMF selects a PCF based on the SUPI. The AMFselects a PCF as described in TS 23.501[2].

16. [optional] AMF to PCF: UE Context Establishment Request ( ).

The AMF request the PCF to apply operator policies for the UE.

17. PCF to AMF: UE Context Establishment Acknowledged ( ).

The PCF acknowledges the UE context establishment request message.

18. [conditional] AMF to SMF: N11 Request ( ).

If the AMF is changed, the new AMF notifies each SMF of the new AMFserving the UE.

The AMF verifies a PDU session status from the UE with the available SMFinformation. In case the AMF has changed, the available SMF informationhas been received from the old AMF. The AMF may request the SMF torelease all network resources related to PDU sessions that are notactive in the UE.

19. SMF to AMF: N11 Response ( ).

The SMF may decide to trigger, for example, UPF relocation. If theregistration type indicated by the UE is periodic registration update,steps 20 and 21 may be omitted.

20. [conditional] AMF to PCF: UE Context Termination Request ( ).

If the old AMF previously requested UE context to be established in thePCF, the old AMF terminates the UE context in the PCF.

21. AMF to PCF: UE Context Termination Acknowledged ( ).

22. AMF to UE: Registration Accept (temporary user ID, registrationarea, mobility restrictions, PDU session status, NSSAI, periodicregistration update timer).

The AMF sends a registration accept message to the UE indicating thatthe registration has been accepted. A temporary user ID is included ifthe AMF allocates a new temporary user ID. Mobility restrictions areincluded in case mobility restrictions apply for the UE. The AMFindicates the PDU session status to the UE. The UE removes any internalresources related to PDU sessions that are not marked with active in thereceived PDU session status. If the PDU session status information wasin the registration request, the AMF shall indicate the PDU sessionstatus to the UE. The NSSAI includes the accepted S-NSSAIs.

23. [conditional] UE to AMF: Registration Complete ( ).

The UE sends a registration complete message to the AMF to acknowledgeif a new temporary user ID was assigned.

Hereinafter, a registration procedure with AMF relocation is described.

FIG. 18 is a flow chart illustrating a NAS message redirection procedureto which the present invention is applicable.

When an AMF receives a registration request, the AMF may need to reroutethe registration request to another AMF (e.g., due to that networkslicing is used and the initial AMF is not the appropriate AMF to servethe UE). The registration with AMF relocation procedure, illustrated inFIG. 18, is used to reroute the NAS message of the UE to the target AMFduring a registration procedure.

A first AMF and a second AMF register its capability at the NRF.

1. Step 1 and 2 of FIG. 4.2.2.2.2-1 of TS 23.501 has occurred, and the(R)AN sends the registration request message within an initial UEmessage to the initial AMF.

2. If the AMF needs the SUPI and/or UE's subscription information todecide whether to reroute the registration request or if theregistration request was not sent integrity protected or integrityprotection is indicated as failed, the AMF can perform step 4 to 14 ofFIG. 4.2.2.2.2-1.

3. [conditional] AMF to NRF: NF Discovery Request (NF type).

The initial AMF decides to reroute the NAS message to another AMF. Ifthe initial AMF does not locally store a target AMF address, the initialAMF sends an NF discovery request to the NRF to find a proper target AMFwhich has required NF capabilities to serve the UE. The NF type is setto AMF.

4. NRF to AMF: NF Discovery Response (list of AMFs, NF capabilities).

The NRF replies with a set of potential target AMFs and theircapabilities. Based on the information about registered NFs and requiredcapabilities, a target AMF is selected by the initial AMF.

5. If the initial AMF, based on local policy and subscriptioninformation, determines to directly forward the NAS message to thetarget AMF, the initial AMF may send a reroute NAS message to the targetAMF. The reroute NAS message includes information enabling (R)AN toidentify the N2 terminating point and the NAS message carried at step 1,and optionally includes the UE's SUPI and MM context. If network slicingis used and the initial AMF updates the NSSAI at step 1, the updatedNSSAI is included. The target AMF then updates the (R)AN with a newupdated N2 termination point for the UE (step 5b), and the (R)ANacknowledges the updated N2 termination point (step 5c). Step 5 may beskipped.

Steps 5b and 5c can occur separately or as part of the firstsubsequently required N2 interaction.

6. If the initial AMF, based on local policy and subscriptioninformation, determines to forward the NAS message to the target AMF viaRAN, the initial AMF sends a reroute NAS message to the RAN (step 6a).The Reroute NAS message includes the information about the target AMFand the registration request message carried at step 1, and optionallyincludes the UE's SUPI and MM context. If network slicing is used andthe initial AMF updates the NSSAI at step 1, the updated NSSAI isincluded in the reroute NAS message. The RAN sends the Initial UEmessage to the target AMF (step 6b).

7. After receiving the registration request message transmitted at step5a or step 6b, the target AMF continues with the registration procedure(with the target AMF corresponding to the new AMF).

Interaction Control Method Between MM and SM

A SM NAS message sent by a UE shall always go through an AMF so that theSM NAS message is sent to a SMF. Thus, the SM message may be sent bybeing attached or piggybacked to a MM or RM message. This is similar tothat a PDN connectivity request message, that is an ESM message, is sentby being piggybacked to an attach request message that is an EMM messagein EPC. In 5GC, a registration procedure similar to an Attach isdefined. A PDU session establishment related message may be or may notbe piggybacked to a registration message.

If the SM message is sent by being piggybacked to the MM message (if theSM message is sent to an initial message), the following problems may becaused.

1) Problem 1

In an initial registration or attach process, if a SM request messagefor PDU session establishment/change, etc. is forwarded together, the UEmay include the following information in a registration request message(or, referred to as UL NAS message).

[Registration Request Message]

-   -   SM message container: PDU session establishment request (DNN,        S-NSSAI(1))    -   SM routing information: S-NSSAI(2) and/or DNN    -   Requested NSSAI: Set of S-NSSAI(3)

Here, S-NSSAI ((1) and (2)) included in SM related items may be S-NSSAIrequested by PDU session, and S-NSSAI (3) included in requested NSSAImay be S-NSSAIs that has to be considered upon registration request.That is, the S-NSSAIs ((1) and (2)) included in the SM may be a subsetof the requested NSSAI. The S-NSSAIs ((1) and (2)) each may be definedas a single parameter, have the same value, and may be included in therequested NSSAI.

The AMF may consider information such as DNN, S-NSSAI, etc. whenselecting an appropriate SMF through a SMF selection function, and theUE may represent the information on the part that the AMF candecipher/recognize, and may provide it to the AMF.

2) Problem 1-1. Handling of SM Message Piggybacked Upon RM/MMRejection—if Registration Itself is Rejected

In the registration procedure, the AMF may reject a registration requestof the UE for various reasons. In this case, the AMF may send a rejectmessage (i.e., registration reject) to the registration request to theUE.

However, unlike the conventional EPC, etc. in which SM and MM weremanaged/handled in MME that is one entity, in 5GC, SM and MM have beendefined to be respectively managed/handled in the SMF and the AMF thatare separated from each other. Therefore, even if the UE receives areject message from the AMF responsible for the managing/handling theMM, the UE cannot know whether to accept/reject the SM message that hasbeen sent upon registration request. That is, the registration requestof the UE is sent to the SMF via the AMF, but if a reject of theregistration request is decided at the AMF, the SM message included inthe corresponding registration request is not forwarded to the SMFenabling to handle a response. As a result, a problem arises that the UEcannot receive a response to the SM message.

3) Problem 1-2. Handling when RM/MM has been Accepted, but a SpecificService has been Rejected—if a Registration has been Accepted, butServices Related to a Specific Session are Rejected

A UE and a network using network slicing request services (or slices) ina registration process and go through an accept process. The networkshall include, in an accept message, S-NSSAI corresponding toservice/slice information requested from the UE through RM request(registration request), i.e., allowable service/slice information afterchecking S-NSSAI included in requested NSSAI. In this instance, theS-NSSAI corresponding to the allowable/acceptable service/sliceinformation may be referred to as allowed NSSAI or accepted NSSAI.

As described above, the network may allow/accept only part ofservice/slice requested by the UE or reject only part. In this instance,the network can handle the registration request of the UE if a PDUsession request for the service/slice is piggybacked together, but thenetwork shall reject a SM request corresponding to the correspondingservice/slice if the network has to reject service/slice to which PDUsession creation is requested. However, if the correspondingservice/slice has been rejected in an access step of the UE (i.e., stepof checking S-NSSAI included in the requested NSSAI and determiningwhether the S-NSSAI is allowable/acceptable service/slice), the AMFcannot forward or may not forward the SM request for the service/sliceto the SMF. Even in this case, the UE can receive a response to theMM/RM request, but cannot receive a response to the SM requestpiggybacked together.

4) Problem 2. Handling in Forwarding Failure Due to MM/RM Layer Problemwhen Forwarding SM Message

Due to the architecture of 5GS or 5GC, in order to forward a SM NASmessage, the SM NAS message shall go through the AMF, and information,etc. on forwarding/routing shall be added to the part that the AMF caninterpret/recognize. Thus, the SM NAS message requires additionalmessage handling before it is forwarded to a lower layer (RRC) as in theconventional technology (EPS, UMTS). If a layer performing the messagehandling is a MM or RM layer, the following problems may arise.

In order to create a new session or manage/release an existing sessionin a SM NAS layer or a sublayer of the UE, the SM NAS message can begenerated. A MM NAS layer of the UE describes/adds additionalinformation (e.g., information such as PDU session ID, DNN and/orS-NSSAI, etc.) to the SM NAS message and encapsulates the SM NASmessage. The encapsulated SM NAS message may be an extended form of a SMmessage or may be a MM/RM message such as MM NAS transport.

5) Problem 2-1. When Problem Occurs in Radio or N2 Section

If the forwarding of a MM/RM message fails or is rejected due to anyproblem in a lower section (e.g., a radio AS section including RRC orRRC lower layer or a N2 section between the RAN and the AMF) in aprocess for sending the MM/RM message to the AMF, the UE is instructedthe forwarding failure from the lower layer before the rejection in theNAS layer. This problem is that because the forwarding failureindication at the lower layer is generally forwarded only up to theMM/RM layer or the layer finally encapsulating the NAS message, the SMlayer generating the SM NAS message cannot recognize it.

6) Problem 2-2. In Case of Rejection at AMF

The MM/RM message or the encapsulated NAS message has been forwarded tothe AMF, but the SM NAS message is not forwarded to the SMF and may berejected due to the problem in terms of RM, access, or AMF. In thisinstance, the AMF sends a reject message to the MM/RM layer of the UE ora layer encapsulating the SM message. However, since the AMF cannotgenerate the SM reject message, the SM layer of the UE cannot receive aresponse to the SM NAS message although it has sent the SM NAS message.

Hereinafter, various methods for solving the above-described problemsare proposed.

<Invention Proposal 1. Interaction Between MM-SM Layers at UE>

The invention proposal 1 is to solve the problems described abovethrough an interaction between several layers or sublayers (e.g., MM,RM, SM, CM, RRC, etc.) within a UE.

Before describing this, in the present specification, a MM layer refersto a layer responsible for overall mobility management and access andmay correspond to a RM layer in 5GS. That is, in the presentspecification, description/embodiments of the MM layer may beequally/similarly applied to the RM layer. The SM layer, the MM layer,etc., may be a sublayer of a NAS layer. In the present specification, aSM (sub)layer, a SM NAS (sub)layer, and a 5GSM (sub)layer may be used inthe same sense, and a MM (sub)layer, a MM NAS (sub)layer, and a 5GMM(sub)layer may be used in the same sense. Further, messages (e.g., MMmessage) that are transmitted and received between the UE and the AMFmay be commonly referred to ‘UL/DL NAS message’ for convenience ofexplanation.

FIG. 19 illustrates a control plane protocol stack of a UE applicable tothe present invention.

Referring to FIG. 19, a SM layer may be located as an upper layer of aMM layer, unlike a related art. Thus, a UE may forward a (5G) SM messagegenerated by the SM layer (within the UE) to the MM layer that is thelower layer. In this instance, a NAS timer at the SM layer of the UE maystart according to a SM procedure to which the corresponding message issent. A timer of different characteristic and length are generallydefined for each SM procedure. Even if multiple SM procedures aresimultaneously performed and the same SM procedure is performed onmultiple sessions, a separate timer may be assigned to each session. Forexample, if PDU session establishment procedures for PDU sessions #1 and#2 are simultaneously performed in parallel/independently, a timer(e.g., T35xx) may be assigned/segmented/initiated for each session orfor another unit defined separately. The timer is defined/configured asa message response waiting time in the corresponding NAS procedure. If atimer expires due to no response within the waiting time, the UE canretransmit the corresponding message by a predetermined number of times.If even the retransmission of the message by the predetermined number oftimes fails, the UE may regard the corresponding procedure as a failureand perform a subsequent operation (e.g., stop a PDU sessionestablishment/change procedure). The subsequent operation may be assumedto be applied similarly to NAS of EPS and EPC and has been described inTS 24.301 and TS 24.008.

A MM NAS layer may piggyback a SM message forwarded from the upper layerto a (5G) MM message including additional information and transmit it tothe lower layer. That is, a (5G) SM message may be piggybacked to aspecific (5G) MM transmission message. To this end, the (5G) SM messagemay be transmitted as an information element of the (5G) MM transmissionmessage. In this case, the UE, the AMF, and the SMF may perform a (5G)MM procedure and a (5G) SM procedure in parallel/independently. Thus,the success of the (5G) MM procedure is irrelevant to the success of thepiggybacked (5G) SM procedure.

The MM layer may also initiate/use a MM NAS timer for managing the MMprocedure. The purpose of the corresponding timer is also the same asthe above-described SM NAS timer, and a subsequent operation upon timerexpiration may be defined for each procedure. The subsequent operationmay be assumed to be applied similarly to NAS of EPS and EPC and hasbeen described in TS 24.301 and TS 24.008.

The MM message forwarded to the lower layer may be sent to the AMF via5G RAN through a radio layer. The MM layer of the AMF receiving themessage may select an appropriate SMF based on SM NAS forwarding/routinginformation included in the MM message and may forward/route thecorresponding MM NAS message or forward/route the corresponding MM NASmessage to the already selected SMF. However, the AMF may reject the MMmessage itself due to problems with the AMF and/or problems at the MMNAS layer. And/or, if there is a problem (e.g., no routing, no servingSMF found, etc.) in the processing of the SM message due to causesrelated to the SM layer, the AMF may reject the MM message.

In this case, the AMF may forward, to the UE, a MM reject message inwhich a reject cause (i.e., MM (reject) cause value/code) isspecified/included. More specifically, if the reject cause is a problemwith the AMF and the MM layer, the AMF may send a cause codeindicating/stating the cause to the UE. If the reject cause is a problemrelated to the SM message processing, the AMF may send a cause codeindicating/stating the cause to the UE. For example, a cause value/codemay be defined as follows.

#XX. SM message handling failure

#YY. No valid SMF available

The cause value/code may be used 1) if the processing in the AMF isimpossible due to the problem of the SMF (e.g., #YY), and 2) ifinformation in the AMF is not sufficient or the processing of the SMmessage is impossible due to the problem of the AMF in a situation wherethe SM message has to be processed (e.g., #XX). However, the presentspecification is not limited thereto, and the cause value/code can bedefined/implemented in various embodiments in order to indicate/statethe reject cause.

If the UE (particularly, the MM NAS layer of the UE) receives a (MM)reject message, the UE can stop a NAS timer that is running for a MMprocedure corresponding to the first rejected MM message. Further, theUE (particularly, the MM NAS layer of the UE) can check the causevalue/code included in the (MM) reject message received from the AMF andtake action (e.g., stop the PDU session establishment/change procedure)according to the cause value/code. The UE (particularly, the MM NASlayer of the UE) can take action (e.g., stop the PDU sessionestablishment/change procedure) according to a case of indicating thatthe cause is related to the AMF. In addition, the UE may forward, to theSM layer that is the upper layer, rejection information/indication thatthe MM procedure has failed/been rejected (i.e., rejectioninformation/indication that the SM message cannot be routed/forwarded).

The rejection information/indication is defined in the form of aninter-layer indication, i.e., is not defined in a separate message type,and may be forwarded to the inter-layer in the form ofinformation/indication itself. The rejection information/indication mayinclude MM failure/rejection information and MM failure/reject cause ifa failure/reject cause is a MM related cause, and may include SMfailure/rejection information (e.g., SM message routingfailure/rejection information and failure/reject cause) if thefailure/reject cause is a SM related cause. In addition, the rejectioninformation/indication may further include other information forfailure/rejection related handling (e.g., back-off timer), and the like.Here, respective information/indication items that can be included inthe rejection information/indication may be selectively included inrejection information/indication depending on its cause and theembodiment implementation.

And/or, if the MM layer of the UE determines that it needs to forwardinformation to the SM layer, the MM layer of the UE may autonomouslygenerate a pseudo-SM message and forward it to the upper layer. Thepseudo-SM message may be sent in the form of a reject message for a (SM)request message had been requested by the SM layer, and may be forwardedto the upper layer, including a SM cause mapped to a cause that the MMlayer receives (from the AMF). For example, if the received MM cause is(temporary) AMF failure/rejection (due to congestion) or the like, theUE (particularly, the MM NAS layer of the UE) may include, in thepseudo-SM message, a timer value similar to a MM back-off timer valuereceived from the SM cause and/or the MM layer indicating a cause suchas the congestion.

The SM layer of the UE may perform a subsequent operation according to a(pseudo-) SM reject message forwarded from the lower layer. Since the SMlayer has received a response (in particular, a reject) to the requestaccording to a fixed timer operation, the SM layer may stop a related SMNAS timer and perform a defined operation. However, it may be limited toa case where the MM layer and the SM layer of the UE use the samesecurity context.

The SM layer receiving the rejection information/indication from the MMlayer that is the lower layer may stop a SM NAS timer (e.g., T3580) fora rejected/failed (NAS) procedure and perform an operation according tothis.

If a reject cause (i.e., MM cause) that the MM layer receives from theAMF is related to MM, the MM layer may inform the SM layer about whethera problem in the MM layer upon the forwarding of the rejectioninformation/indication is temporary or permanent. If a reject cause thatthe MM layer receives from the AMF is related to SM (i.e., SM cause),the MM layer of the UE may inform the SM layer about a detailed SMreject cause upon the forwarding of the rejectioninformation/indication. That is, the MM layer may inform that therejection of the MM layer (i.e., no routing/forwarding of the SMmessage) is due to impossibility/failure/rejection (i.e., the detailedcause) of the SM related processing of the AMF.

If a failure/reject cause is permanent, the SM layer of the UE mayperform a release procedure for a session or a DN, etc. requesting thecorresponding SM message. And/or, the SM layer of the UE may manage thesession or the DN by including the corresponding session or the DN in aforbidden list, not to perform an additional procedure on thecorresponding session or the DN, etc. If a service for the correspondingsession is absolutely necessary, the SM layer of the UE may requestderegistration to the MM layer and trigger a procedure for searching newPLMN.

<Invention Proposal 1-1. SM or MM with Specific Service RejectionAccepted>

In case of using network slicing as in scenario presented in the problem1-2, even if a MM procedure is accepted, detail service/slice requestedthrough the corresponding MM procedure may be rejected. If a request ofcreating a PDU session is piggybacked, services requested by thecorresponding PDU session may be included in a SM request in the form ofS-NSSAI and may also be included in a requested NSSAI list included in aMM request message.

Based on the invention proposal 1, it may be assumed that the UE sends aregistration or a MM request/message, that piggybacks a SM message, to anetwork, and the network accepts the registration or the MMrequest/message, but rejects a service that is individually requestedfrom the corresponding request/message. In this instance, if therejected service is a service of a SM request through the piggybacked SMmessage, the AMF may operate as follows.

The AMF can perform verification and authorization on a requested NSSAIincluded in the MM request/message and determine allowed NSSAI/acceptedNSSAI for the UE. If a SM request/message and S-NSSAI corresponding tothe SM request/message are specified in the MM request/message, the AMFfirst performs a NSSAI verification procedure before forwarding the SMmessage to the SMF, and shall check whether services of thecorresponding S-NSSAI service are allowed to the UE. If the verificationtarget S-NSSAI is not included in the allowed/accepted NSSAI, the AMFmay discard the SM message corresponding to the verification targetS-NSSAI and send a MM accept message for the MM request/message to theUE.

The MM accept message may include allowed/accepted (S-)NSSAIinformation, rejected (S-)NSSAI information, and/or a reject cause.Further, the MM accept message may include information about whether arejection for (S-)NSSAI is temporary or permanent, and/or a moredetailed reject cause. In addition, if the AMF rejects the (S-) NSSAIfor a temporary cause such as congestion, the AMF may transmit aback-off timer value by including the back-off timer value in the MMaccept message.

If the SM request/message receives the piggybacked MM request/message,the AMF may include information indicating, that the S-NSSAI requestedvia the corresponding SM request/message has been rejected, in SMrelated information (within the MM accept message for the MMrequest/message). This may be included in the form of a predefinedbit/flag indication, an SM cause, or the following MM cause. In thisinstance, a MM cause value is a special case and may represent/mean areject cause for the piggybacked SM request/message, not a rejection forthe MM request/message. Configuration examples of the cause may beimplemented in the following embodiments.

#XX. Piggybacked SM message rejected.

#YY. S-NSSAI for piggybacked SM message not allowed.

If the UE receives a MM accept response from the AMF, the UE may processit similar to the manner proposed in the invention proposal 1. The MMlayer may inform the SM layer of a rejection based on informationreceived from the AMF, and the rejection may be forwarded in the form ofindication/information or a pseudo-SM message as proposed in theinvention proposal 1. However, in the case, since the MM procedure hassucceeded, information forwarded to the SM layer may be limited toinformation on SM failure/rejection. If the SM layer receives theinformation on SM failure/rejection from the lower layer, the SM layerstops a timer (e.g., T3580) and performs a predefinedadditional/subsequent operation according to received information.

<Invention Proposal 1-2. Interaction Between SM Layer, MM Layer, and ASLayer>

There may occur a case where a MM request message does not reach an AMFin a process for sending a MM message due to problems of ASlayer/segment and/or N2 layer/segment. This may be due to a radio linkforwarding/routing failure, a forwarding/routing failure due to aspecific reason of the AS layer/segment, and/or a forwarding/routingfailure due to a specific reason of the N2 layer/segment, and the like.If the AS layer/segment has recognized such a failure, the ASlayer/segment may notify the upper layer of it.

A MM layer may perform an operation according to a failure relatedindication (lower layer indication)/information received from the lowerlayer (e.g., the AS layer/segment). If a SM message has been piggybackedand transmitted to the MM message, the MM layer may forwardforwarding/routing failure indication/information to the SM layer. Thefailure indication/information is forwarded using the method proposed inthe invention proposal 1, but a failure cause to be forwarded may bedifferentiated from that in the invention proposal 1. For example, thefailure cause may be forwarded to the SM layer as indication/informationrepresenting a lower layer (forwarding/routing) failure, etc. (#XX), ormay be forwarded to the SM layer via a pseudo-SM message as a causevalue/code representing a lower layer (forwarding/routing) failure, etc.

<Invention Proposal 1-3. Interaction Between SM Layer and NAS Sublayer>

FIG. 20 illustrates a control plane protocol stack within a UE accordingto an embodiment of the present invention.

An NAS sublayer newly defined/proposed in FIG. 20 is a sublayer capableof supporting both MM and SM and may be responsible for reliable NASmessage forwarding between core-UE.

Upon protocol stack application of the invention proposal 1-3, aninteraction between a MM layer and a SM layer among the operationsproposed in the invention proposals 1, 1-1, and 1-2 may be applied tothe NAS sublayer. That is, the interaction between the MM layer and theSM layer proposed above may be controlled/performed by the NAS sublayer,and the invention proposal 1-3 is different from the invention proposals1, 1-1, and 1-2 in that information delivery to the SM layer, which hasbeen performed by the MM layer, is performed by the NAS sublayer (i.e.,information delivery from the MM layer to the SM layer via the NASsublayer). Thus, information delivered to the SM layer by the NASsublayer and an information delivery manner are similar to theembodiments proposed above.

<Invention Proposal 2. AMF Handling/Control of SM Procedure>

The invention proposal 2 is to solve problems described above through aSM procedure handling/control of an AMF.

Before describing this, in the present specification, a MM layer refersto a layer responsible for overall mobility management and access andmay correspond to a RM layer in 5GS. That is, in the presentspecification, description/embodiments of the MM layer may beequally/similarly applied to the RM layer. The SM layer, the MM layer,etc., may be a sublayer of a NAS layer. In the present specification, aSM (sub)layer, a SM NAS (sub)layer, and a 5GSM (sub)layer may be used inthe same sense, and a MM (sub)layer, a MM NAS (sub)layer, and a 5GMM(sub)layer may be used in the same sense. Further, messages (e.g., MMmessage) that are transmitted and received between the UE and the AMFmay be commonly referred to ‘UL/DL NAS message’ for convenience ofexplanation.

The AMF cannot currently recognize a SM message (which is transparent toAMF) and can determine only forwarding/routing of the SM message basedon SM related information added to the outside of the SM message.Therefore, the AMF has a limitation in performing an operation relatedto the SM, which causes the above-described problems.

In order to solve the problems, a SMF (hereinafter referred to as ‘SMFfor error’) of special purpose for handling/processing an error, such asa case where the AMF cannot route/forward a SM request/message to theSMF or a case where a requested service itself is not allowed, can benewly defined separately. The ‘SMF for error’ may not have a functionfor a normal session management/procedure and may be defined as an SMFthat performs only an operation for coping with a SM (request/message)rejection case (or the above-described error case, etc.). And/or, theoperation/function of the ‘SMF for error’ may be implemented/performedin a ‘default SMF’.

As pointed out above, if there occurs a failure/rejection case, such asa case where MM/SM fails/is rejected at the AMF or a case where servicesare rejected at the AMF, the AMF may send a received SM message to the‘SMF for error’. Such an operation may be previously defined by networkoperator's policy and/or configuration. The AMF may additionallydeliver, to the ‘SMF for error’, information about a problem situation(i.e., routing/forwarding failure situation of the SM message) and/or afailure/reject cause through an N11 message, when sending the SM messageto the ‘SMF for error’.

The ‘SMF for error’ may generate a SM reject message based oninformation received from the AMF and/or information included in the SMmessage and send it to the AMF. The AMF may send by piggybacking the SMreject message to a MM reject/accept message upon MM reject/accept. Inthis case, the MM layer and the SM layer of the UE each may perform anadditional operation/procedure according to a network response (i.e.,the MM reject/accept message). In this instance, the additionaloperation/procedure is as described in TS 23.502, and a detailedoperation of the NAS layer is assumed to be similar to NAS of EPS andEPC and is described in TS 24.301 and TS 24.008.

<Invention Proposal 2-1. SM Sublayer within AMF>

FIG. 21 illustrates a control plane protocol stack within a UE accordingto an embodiment of the present invention.

Referring to FIG. 21, a function of the ‘SMF for error’ proposed in theinvention proposal 2 may be implemented as a sublayer of the AMF not aseparately defined SMF. In this case, the AMF can perform errorprocessing/handling using a SM sublayer implemented inside the AMFwithout an interaction with the separate SMF. The function/operation ofthe SM sublayer may be the same as ‘SMF for error’ described in theinvention proposal 2.

It is possible to locally release (implicitly) a PDU session at the CNside for a specific cause, and the AMF can remove a context of thelocally released PDU session. In this instance, if the UE is in aCM-IDLE state, the UE can maintain the context for the corresponding PDUsession as a result of not receiving an explicit release message for thecorresponding PDU session. Afterwards, the UE can perform the followingMM procedure including/using a corresponding PDU session ID, in order toreceive services with the corresponding PDU session (e.g., if MO data isgenerated).

-   -   Registration update (PDU session activation)    -   Service request (PDU session activation)

However, the corresponding PDU session is already in a locally releasedstate at the CN, and there is no serving SMF information for thecorresponding PDU session at the AMF. That is, there arises a problemthat the UE unnecessarily performs/initiates a MM procedure for thealready released PDU session. As one method for solving the problem, amethod may be proposed to allow the UE to know whether to locallyrelease the PDU session through the PDU session status exchange betweenthe UE and the AMF. However, even in this instance, since the UE cannotstill know a local release cause of the PDU session, there may arise aproblem that the UE performs/initiates again the MM procedure for thereleased PDU session. For example, the PDU session may be locallyreleased for a cause such as a release due to a specific SMF problem,change in user's subscription information (within UDM), and/or change insubscription information at the AMF. However, since the UE does not knowa release cause, the UE may request again the establishment of the PDUsession. Further, if the PDU session is released due to a cause such asa local area data network (LADN) and mobility limitation (e.g., LADNregion deviation, non-allowed region entry, etc.), the AMF can know therelease of the PDU session and adjust PDU session statussynchronization. However, there is a problem that the UE cannot beinformed of it (SM/MM separation).

Accordingly, a method for solving the problem is proposed below withreference to FIG. 22.

FIG. 22 is a flow chart illustrating an application example of theinvention proposal 2 if PDU session synchronization fails.

1. First, PDU session X may be established between a UE and SMF1.

2a. Next, the UE may enter a CM-IDLE state.

2b. Next, the PDU session X may be released without explicit/implicitsignaling with the UE (local release).

3a. In case of a PDU session local release requiring an additionaloperation not a normal PDU session local release, the SMF1 may forward arelease cause to an AMF via a N11 message. In particular, the N11message may include a locally released PDU session ID, a local releaseindication (ind), and/or a release cause.

3b. If the AMF is connected to ‘SMF2 (SMF for error)’ proposed in theinvention proposal 2 (or if a SMF sublayer proposed in the inventionproposal 2-1 is implemented), the AMF may transmit information receivedfrom the SMF1 in the 3a to the SMF2 (or the SMF sublayer). That is, theinformation received from the SMF1 may be transmitted to the SMF2 in theform of N11-N11 message delivery through the AMF. In this case, the SMF1may specify/indicate a target SMF (i.e., SMF2) address or ID to the AMF.

3c. If an interface exists between the SMFs, the release cause andlocally released PDU session ID information may be transmitted from SMF1to the SMF2 in the form of context delivery.

That is, one of the steps 3b and 3c may be selectively performedaccording to an embodiment.

3d. If the AMF receives the N11 message through the step 3a, the AMF mayupdate a serving SMF mapping for a PDU session that has been currentlystored. In this case, the AMF may specify and store/update SMF2 (i.e.,‘SMF for error’) as a serving AMF corresponding to the indicated PDUsession ID through the received N11 message, or specify and store/updatethat the PDU session corresponding to the indicated PDU session ID hasbeen locally released.

4. If the UE has requested activation for the already locally releasedPDU session, the AMF may perform the following operation, if necessaryor desired.

If it is reported that the SMF2 mapped to the PDU session requested bythe UE is SMF2 (i.e., SMF for error) or is locally released:

5. The AMF may forward a PDU session activation request to the SMF2 viaa N11 request message.

6-7. The SMF2 may forward, to the UE, an activation reject for thealready locally released PDU session through the AMF using a N11response message. In this instance, the SMF2 may also forward, to theUE, the release cause received through the step 3b or 3c. If it isnecessary to limit the retry of the UE, the SMF2 may also forward, tothe UE, a retry back-off timer value for the locally released PDUsession.

If the PDU session requested by the UE is locally released without anyaction:

The AMF may update a PDU session status field and send a service acceptor reject message to the UE.

<Invention Proposal 3. Applicability for Non-3GPP Access

5G RAN, 5G AS, 5G RRC, etc. specified in the invention proposals 1 and 2have been specified to be described based on 3GPP access, i.e., NR, 5GLTE, and 5G-RAN, but are not limited thereto. They may beequally/similarly applied to non-3GPP access. In this case, the role of5G RAN may be replaced by N3IWF, and RRC may correspond to the lowerlayer of NAS.

FIG. 23 is a flow chart illustrating a method for sending a NAS messageof a UE according to an embodiment of the present invention. Theembodiment/description proposed in the invention proposal 1 may beequally applied to the flow chart, and duplicate description is omitted.

First, a UE may send an UL NAS message including a SM message to an AMFin S2310. In this instance, the SM message may be a message forperforming a request (e.g., PDU session establishment/change, etc.)related to a PDU session. The SM message may be generated in a SMsublayer within the UE and forwarded to a MM sublayer that is a lowerlayer of the SM sublayer, and the UL NAS message including the SMmessage may be sent to the AMF by the MM sublayer. Here, the SM sublayermay correspond to a sublayer for PDU session control that is defined inthe UE, and the MM sublayer may correspond to a sublayer for mobilitycontrol of the UE that is defined in the UE. The UL NAS message mayfurther include DNN and/or S-NSSAI used for the selection of a SMF toforward the SM message. Further, if the SM message is a messagerequesting an establishment of the PDU session, the UL NAS message mayfurther include a PDU session ID for the PDU session to which theestablishment is requested.

Next, the UE may receive, from the AMF, an indication message indicatingthat the SM message is unroutable, in S2320. The indication message mayadditionally include an unroutable cause value of the SM message.Indication information indicating that the SM message is unroutable maybe generated by the MM sublayer receiving the indication message andtransmitted to the SM sublayer of the UE. In this instance, the MMsublayer may deliver, to the SM sublayer, information about whether theunroutable SM message is permanent or temporary, together with theindication information. If the unroutable SM message is permanent, theSM sublayer may perform a release procedure for a PDU session and/or DNrelated to the SM message. Furthermore, the SM sublayer may include thecorresponding PDU session and/or DN in a procedure forbidden list andmanage them, not to perform an additional procedure for thecorresponding PDU session and/or DN (particularly, identificationinformation for the corresponding PDU session and/or DN). If servicesrelated to the corresponding PDU session and/or DN are required, the SMsublayer may request deregistration to the MM sublayer and trigger aprocedure for searching new PLMN.

If the SM sublayer forwards the SM message to the MM sublayer, apre-configured timer may start. If the SM sublayer receives theindication information from the MM sublayer before the timer expires,the SM sublayer may stop the timer and stop a procedure (e.g., PDUsession establishment/change procedure, etc.) related to the SM message.If the timer expires, the SM sublayer may retransmit the SM message tothe MM sublayer by a predetermined number of times. If theretransmission by the predetermined number of times fails, the SMsublayer may stop the procedure (e.g., PDU session establishment/changeprocedure, etc.) related to the SM message.

FIG. 24 is a flow chart illustrating a method for sending a NAS messageof an AMF according to an embodiment of the present invention. Theembodiment/description proposed in the invention proposal 2 may beequally applied to the flow chart, and duplicate description is omitted.

First, an AMF may receive, from a UE, an UL NAS message including a SMmessage for a PDU session related request (e.g., PDU sessionestablishment/change, etc.) in S2410. The UL NAS message may correspondto a MM message in which the SM message is included/piggybacked.

Next, if the AMF decides that the SM message is unroutable to a firstSMF that is a forwarding target of the SM message, the AMF may forwardthe SM message to a pre-configured second SMF in S2420. In thisinstance, the AMF may decide that the SM message is unroutable based onvarious causes. For example, if a PDU session related request target viathe SM message is an already locally released PDU session, the AMF maydecide that the SM message is unroutable to the first SMF. The SMmessage may be forwarded to the second SMF via a first N11 message.Further, an unroutable cause of the SM message together with the SMmessage may be forwarded to the second SMF via the first N11 message.

Next, the AMF may receive a SM reject message for the SM message fromthe second SMF in S2430. Here, the second SMF may be a SMF definedindependently from the first SMF, in order to process the unroutable SMmessage. The second SMF may be implemented as a NAS sublayer within theAMF not a default SMF or a separate SMF according to an embodiment.

Next, the AMF may send a DL NAS message including the SM reject messageto the UE.

Although not shown in the flow chart, the AMF may receive a retryback-off timer value of the PDU session related request from the secondSMF.

If a PDU session is locally released, the AMF may receive a second N11message from the first SMF. In this instance, the second N11 message mayinclude an ID, a local release indication, and/or a local release causeof the PDU session. In this case, the AMF may update status (e.g., arelease status) information of the locally released PDU session based onthe received second N11 message. The ID, the local release indication,and/or the local release cause of the PDU session may be delivered fromthe AMF to the second SMF or from the first SMF to the second SMF.

Since the inventions proposed above enables interaction/informationexchange between NAS layers/entities in preparation for various messageforwarding/routing failure situations that may occur when the SM layerprocedure and the MM layer procedure in 5GS and 5GC are independentlyseparated and are simultaneously performed, they can improve the messageforwarding reliability/efficiency of the UE and the network and solvevarious problems resulting from the message forwarding/routing failure.

Overview of Device to which the Present Invention is Applicable

FIG. 25 illustrates a block configuration diagram of a communicationdevice according to an embodiment of the present invention.

Referring to FIG. 25, a wireless communication system includes a networknode 2510 and a plurality of UEs 2520.

The network node 2510 includes a processor 2511, a memory 2512, and acommunication module 2513. The processor 2511 implements functions,processes, and/or methods proposed above. Layers of wired/wirelessinterface protocol may be implemented by the processor 2511. The memory2512 is connected to the processor 2511 and stores various types ofinformation for driving the processor 2511. The communication module2513 is connected to the processor 2511 and transmits and/or receiveswired/wireless signals. An example of the network node 2510 maycorrespond to a base station, MME, HSS, SGW, PGW, an application server,or the like. In particular, if the network node 2510 is the basestation, the communication module 2513 may include a radio frequency(RF) unit for transmitting/receiving a radio signal.

The UE 2520 includes a processor 2521, a memory 2522, and acommunication module (or RF unit) 2523. The processor 2521 implementsfunctions, processes, and/or methods proposed above. Layers of a radiointerface protocol may be implemented by the processor 2521. The memory2522 is connected to the processor 2521 and stores various types ofinformation for driving the processor 2521. The communication module2523 is connected to the processor 2521 and transmits and/or receives aradio signal.

The memories 2512 and 2522 may be inside or outside the processors 2511and 2521 and may be connected to the processors 2511 and 2521 throughvarious well-known means. Further, the network node 2510 (in case of thebase station) and/or the UE 2520 may have a single antenna or multipleantennas.

FIG. 26 illustrates a block configuration diagram of a communicationdevice according to an embodiment of the present invention.

In particular, FIG. 26 illustrates in more detail the UE illustrated inFIG. 25.

Referring to FIG. 26, the UE may include a processor (or digital signalprocessor (DSP)) 2610, an RF module (or RF unit) 2635, a powermanagement module 2605, an antenna 2640, a battery 2655, a display 2615,a keypad 2620, a memory 2630, a subscriber identification module (SIM)card 2625 (which is optional), a speaker 2645, and a microphone 2650.The UE may also include a single antenna or multiple antennas.

The processor 2610 implements functions, processes, and/or methodsproposed above. Layers of a radio interface protocol may be implementedby the processor 2610.

The memory 2630 is connected to the processor 2610 and storesinformation related to operations of the processor 2610. The memory 2630may be inside or outside the processor 2610 and may be connected to theprocessors 2610 through various well-known means.

A user inputs instructional information, such as a telephone number, forexample, by pushing (or touching) buttons of the keypad 2620 or by voiceactivation using the microphone 2650. The processor 2610 receives andprocesses the instructional information to perform an appropriatefunction, such as to dial the telephone number. Operational data may beextracted from the SIM card 2625 or the memory 2630. Further, theprocessor 2610 may display instructional information or operationalinformation on the display 2615 for the user's reference andconvenience.

The RF module 2635 is connected to the processor 2610 and transmitsand/or receives an RF signal. The processor 2610 forwards instructionalinformation to the RF module 2635 in order to initiate communication,for example, transmit a radio signal configuring voice communicationdata. The RF module 2635 includes a receiver and a transmitter toreceive and transmit the radio signal. The antenna 2640 functions totransmit and receive the radio signal. Upon reception of the radiosignal, the RF module 2635 may transfer a signal to be processed by theprocessor 2610 and convert the signal into a baseband. The processedsignal may be converted into audible or readable information output viathe speaker 2645.

The embodiments described above are implemented by combinations ofcomponents and features of the present invention in predetermined forms.Each component or feature should be considered selectively unlessspecified separately. Each component or feature may be carried outwithout being combined with another component or feature. Moreover, somecomponents and/or features are combined with each other and canimplement embodiments of the present invention. The order of operationsdescribed in embodiments of the present invention may be changed. Somecomponents or features of one embodiment may be included in anotherembodiment, or may be replaced by corresponding components or featuresof another embodiment. It is apparent that some claims referring tospecific claims may be combined with another claims referring to theclaims other than the specific claims to constitute the embodiment oradd new claims by means of amendment after the application is filed.

Embodiments of the present invention can be implemented by variousmeans, for example, hardware, firmware, software, or combinationsthereof. When embodiments are implemented by hardware, one embodiment ofthe present invention can be implemented by one or more applicationspecific integrated circuits (ASICs), digital signal processors (DSPs),digital signal processing devices (DSPDs), programmable logic devices(PLDs), field programmable gate arrays (FPGAs), processors, controllers,microcontrollers, microprocessors, and the like.

When embodiments are implemented by firmware or software, one embodimentof the present invention can be implemented by modules, procedures,functions, etc. performing functions or operations described above.Software code can be stored in a memory and can be driven by aprocessor. The memory is provided inside or outside the processor andcan exchange data with the processor by various well-known means.

It is apparent to those skilled in the art that the present inventioncan be embodied in other specific forms without departing from essentialfeatures of the present invention. Accordingly, the aforementioneddetailed description should not be construed as limiting in all aspectsand should be considered as illustrative. The scope of the presentinvention should be determined by rational construing of the appendedclaims, and all modifications within an equivalent scope of the presentinvention are included in the scope of the present invention.

INDUSTRIAL APPLICABILITY

Although the present invention has been described focusing on examplesapplying to the 3GPP LTE/LTE-A/NR (5G) system, it can be applied tovarious wireless communication systems other than the 3GPP LTE/LTE-A/NR(5G) system.

1. A method for forwarding a non-access stratum (NAS) message of a userequipment (UE) in a wireless communication system, the methodcomprising: sending, to an access and mobility management function(AMF), an uplink (UL) NAS message including a session management (SM)message; and receiving, from the AMF, an indication message indicatingthat the SM message was not forwarded due to routing failure, whereinindication information indicating that the SM message was not forwardeddue to routing failure is forwarded to a SM sublayer of the UE, whereinthe SM message is generated in the SM sublayer and is forwarded to a MMsublayer that is a lower layer of the SM sublayer, wherein the UL NASmessage including the SM message is sent to the AMF by the MM sublayer.2. (canceled)
 3. The method of claim 1, wherein the SM sublayercorresponds to a sublayer that is defined for a protocol data unit (PDU)session control in the UE, wherein the MM sublayer corresponds to asublayer that is defined for a mobility control of the UE in the UE. 4.The method of claim 3, further comprising: starting a pre-configuredtimer, if the SM sublayer forwards the SM message to the MM sublayer;and stopping the timer and stopping a procedure related to the SMmessage, if the indication information is received from the MM sublayerbefore the timer expires.
 5. The method of claim 4, further comprising:retransmitting, by the SM sublayer, the SM message to the MM sublayer bya predetermined number of times, if the timer expires; and stopping aprocedure related to the SM message, if the retransmission by thepredetermined number of times fails.
 6. The method of claim 5, whereinthe UL NAS message further includes a data network name (DNN) and/orsingle network slice selection assistance information (S-NSSAI) used forthe selection of a session management function (SMF) to forward the SMmessage.
 7. The method of claim 5, wherein if the SM message is amessage requesting an establishment of the PDU session, the UL NASmessage further includes a PDU session identifier (ID) for the PDUsession to which the establishment is requested.
 8. The method of claim5, wherein the MM sublayer forwards, to the SM sublayer, informationabout whether the SM message being not forwarded due to routing failureis permanent or temporary, together with the indication information. 9.The method of claim 8, wherein if the SM message being not forwarded dueto routing failure is permanent, the SM sublayer performs a releaseprocedure for a PDU session and/or a data network (DN) related to the SMmessage.
 10. The method of claim 9, wherein the SM sublayer includes thePDU session and/or the DN in a procedure forbidden list and manages thePDU session and/or the DN.
 11. The method of claim 9, wherein ifservices related to the PDU session and/or the DN are required, the SMsublayer requests a deregistration to the MM sublayer.
 12. A userequipment (UE) performing an interworking method between networks in awireless communication system, the UE comprising: a transceiver; atleast one processor; and at least one computer memory operablyconnectable to the at least one processor and storing instructions that,when executed by the at least one processor, perform operationscomprising: sending, via the transceiver to an access and mobilitymanagement function (AMF), an uplink (UL) NAS message including asession management (SM) message; and receiving, via the transceiver fromthe AMF, an indication message indicating that the SM message was notforwarded due to routing failure, wherein indication informationindicating that the SM message was not forwarded due to routing failureis forwarded to a SM sublayer of the UE, wherein the SM message isgenerated in the SM sublayer and is forwarded to a MM sublayer that is alower layer of the SM sublayer, wherein the UL NAS message including theSM message is sent to the AMF by the MM sublayer.
 13. (canceled)
 14. TheUE of claim 12, wherein the SM sublayer corresponds to a sublayer thatis defined for a protocol data unit (PDU) session control in the UE,wherein the MM sublayer corresponds to a sublayer that is defined for amobility control of the UE in the UE.
 15. The UE of claim 14, whereinthe SM sublayer is configured to: start a pre-configured timer, if theSM sublayer forwards the SM message to the MM sublayer; and stop thetimer and stop a procedure for establishing the PDU session, if theindication information is received from the MM sublayer before the timerexpires.